Systems and methods for a split exhaust engine system

ABSTRACT

Methods and systems are provided for operating a split exhaust engine system that provides blowthrough air and exhaust gas recirculation to an intake passage via a first exhaust manifold and exhaust gas to an exhaust passage via a second exhaust manifold. In one example, in response to a request to shut down the split exhaust engine system, an intake throttle may be closed and a first valve disposed in a secondary flow passage coupled between the intake manifold, downstream of the intake throttle, and a first exhaust manifold coupled to a first set of exhaust valves, may be opened. As a result, unburned hydrocarbons may be routed to a catalyst disposed in the exhaust passage.

FIELD

The present description relates generally to methods and systems for asplit exhaust engine including exhaust gas recirculation.

BACKGROUND/SUMMARY

Engines may use boosting devices, such as turbochargers, to increaseengine power density. However, engine knock may occur due to increasedcombustion temperatures. Knock is especially problematic under boostedconditions due to high charge temperatures. The inventors herein haverecognized that utilizing an engine system with a split exhaust system,where a first exhaust manifold routes exhaust gas recirculation (EGR) toan intake of the engine, upstream of a compressor of the turbocharger,and where a second exhaust manifold routes exhaust to a turbine of theturbocharger in an exhaust of the engine, may decrease knock andincrease engine efficiency. In such an engine system, each cylinder mayinclude two intake valves and two exhaust valves, where a first set ofcylinder exhaust valves (e.g., scavenge exhaust valves) exclusivelycoupled to the first exhaust manifold may be operated at a differenttiming than a second set of cylinder exhaust valves (e.g., blowdownexhaust valves) exclusively coupled to the second exhaust manifold,thereby isolating a scavenging portion and blowdown portion of exhaustgases. The timing of the first set of cylinder exhaust valves may alsobe coordinated with a timing of cylinder intake valves to create apositive valve overlap period where fresh intake air (or a mixture offresh intake air and EGR), referred to as blowthrough, may flow throughthe cylinders and back to the intake, upstream of the compressor, via anEGR passage coupled to the first exhaust manifold. Blowthrough air mayremove residual exhaust gases from within the cylinders (referred to asscavenging). The inventors herein have recognized that by flowing afirst portion of the exhaust gas (e.g., higher pressure exhaust) throughthe turbine and a higher pressure exhaust passage and flowing a secondportion of the exhaust gas (e.g., lower pressure exhaust) andblowthrough air to the compressor inlet, combustion temperatures can bereduced while improving the turbine's work efficiency and engine torque.

However, the inventors herein have recognized potential issues with suchsystems. As one example, when shutting down the engine (either during akey off event or as an engine start/stop event) hydrocarbons may resultfrom unburned gases and rotation reversal of the engine may occur(resulting in engine shaking).

In one example, the issues described above may be addressed by a methodfor an engine comprising: in response to a request to shut down theengine: closing an intake throttle and opening a first valve disposed ina secondary flow passage coupled between an intake manifold, downstreamof the intake throttle, and a first exhaust manifold coupled to a firstset of exhaust valves to route unburned hydrocarbons to a catalystdisposed in an exhaust passage coupled to a second set of exhaustvalves. For example, the request to shut down the engine may be a keyoff request. As a result of this operation, unburned hydrocarbons may bedirected to the catalyst, thereby reducing hydrocarbons in the enginesystem and maintaining the catalyst at stoichiometry. Further, byclosing the intake throttle, engine reversal is reduced. Additionally,by opening the second valve and the intake throttle after the engine hasstopped rotating, less exhaust gas recirculation (EGR) may be pulledback into the intake.

As another example, the issues described above may be address by amethod for an engine comprising: in response to a request to shut downthe engine: deactivating all valves of a first set of exhaust valvesconfigured to flow exhaust to an exhaust passage via a first exhaustmanifold; and opening a first valve disposed in a flow passage coupledbetween an intake passage and a second exhaust manifold, where a secondset of exhaust valves are coupled exclusively to the second exhaustmanifold. For example, the request to shut down the engine may be astart/stop request generated responsive to the vehicle in which theengine is installed being stopped. By deactivating the first set ofexhaust valves, gases may be recirculated via the second set of exhaustvalves, thereby running down the pressure in the intake manifold. Thismay improve engine operation upon restart, at which time the first setof exhaust valves may be reactivated.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a schematic depiction of a turbocharged engine system witha split exhaust system.

FIG. 1B shows an embodiment of a cylinder of the engine system of FIG.1A.

FIG. 2A shows a block diagram of a first embodiment of an engineair-fuel ratio control system for an internal combustion engine and anair-fuel ratio flowing into an exhaust gas emissions device.

FIG. 2B shows a block diagram of a second embodiment of an engineair-fuel ratio control system for an internal combustion engine and anair-fuel ratio flowing into an exhaust gas emissions device.

FIG. 3A shows example cylinder intake valve and exhaust valve timingsfor one engine cylinder of a split exhaust engine system.

FIG. 3B shows example adjustments to the intake valve and exhaust valvetimings for one engine cylinder of the split exhaust engine system fordifferent engine operating modes.

FIGS. 4A-4B show a flow chart of a method for operating a split exhaustengine system, where a first exhaust manifold routes exhaust gas andblowthrough air to an intake of the engine system and a second exhaustmanifold routes exhaust to an exhaust of the engine system, underdifferent vehicle and engine operating modes.

FIG. 5 shows a flow chart of a method for operating the split exhaustengine system in a cold start mode.

FIG. 6 shows a flow chart of a method for operating the split exhaustengine system in a deceleration fuel shut-off mode.

FIGS. 7A-7B show a flow chart of a method for operating the splitexhaust engine system in a part throttle mode.

FIG. 8 shows a flow chart of a method for operating the split exhaustengine system in an electric boost mode.

FIG. 9 shows a flow chart of a method for operating the split exhaustengine system in a compressor threshold mode.

FIG. 10 shows a flow chart of a method for operating the split exhaustengine system in a baseline blowthrough combustion cooling (BTCC) mode.

FIG. 11 shows a flow chart of a method for diagnosing one or more valvesof the split exhaust engine system based on scavenge manifold pressure.

FIG. 12 shows a flow chart of a method for controlling EGR flow andblowthrough air to an intake passage from a scavenge manifold viaadjusting operation of one or more valves of the split exhaust enginesystem.

FIG. 13 shows a flow chart of a method for selecting between operatingmodes to adjust a flow of exhaust gases from engine cylinders to anintake passage via scavenge exhaust valves and a scavenge exhaustmanifold of the split exhaust engine system.

FIG. 14 shows a flow chart of a method for operating a hybrid electricvehicle including the split exhaust engine system in an electric mode.

FIG. 15 shows a flowchart of a method for operating the split exhaustengine system in a shutdown mode.

FIG. 16 shows an example graph of changes in engine operating parametersduring operating the split exhaust engine system in a cold start mode.

FIG. 17 shows an example graph of changes in engine operating parametersduring operating the split exhaust engine system in a deceleration fuelshut-off (DFSO) mode.

FIGS. 18A-18B show an example graph of changes in engine operatingparameters during operating the split exhaust engine system in a partthrottle mode.

FIG. 19 shows an example graph of changes in engine operating parametersduring operating the split exhaust engine system in an electric boostmode.

FIG. 20 shows an example graph of changes in engine operating parametersduring operating the split exhaust engine system in a compressorthreshold mode.

FIG. 21 shows an example graph of changes in pressure and oxygen contentof a scavenge exhaust manifold over a single engine cycle of the splitexhaust engine system.

FIG. 22 shows an example graph of controlling one or more engineactuators to adjust exhaust gas recirculation (EGR) flow and blowthroughflow to an intake passage of the split exhaust engine system fromscavenge exhaust valves of engine cylinders.

FIG. 23 shows an example graph of operating a hybrid electric vehicle inan electric mode to heat the split exhaust engine system prior tostarting the engine.

FIG. 24 shows an example graph of changes in engine operating parametersduring operating the split exhaust engine in a shutdown mode.

FIG. 25 shows an example graph of operation of the split exhaust enginesystem from startup to shutdown.

DETAILED DESCRIPTION

The following description relates to systems and methods for operating asplit exhaust engine with blowthrough and exhaust gas recirculation(EGR) to an intake via a first exhaust manifold. As shown in FIG. 1A,the split exhaust engine may include a first exhaust manifold (referredto herein as a scavenge exhaust manifold) coupled exclusively to ascavenge exhaust valve of each cylinder. The scavenge manifold iscoupled to the intake passage, upstream of a turbocharger compressor,via a first EGR passage including a first EGR valve (referred to hereinas a BTCC valve). The split exhaust engine also include a second exhaustmanifold (referred to herein as a blowdown exhaust manifold) coupledexclusively to a blowdown exhaust valve of each cylinder. The blowdownmanifold is coupled to an exhaust passage of the engine, where theexhaust passage includes a turbocharger turbine and one or more emissioncontrol devices (which may include one or more catalysts). In someembodiments, the split exhaust engine system may include additionalpassages coupled between the scavenge manifold and either the intake orexhaust passage, as shown in FIG. 1A. Additionally, in some embodiments,the split exhaust engine system may include various valve actuationmechanisms and may be installed in a hybrid vehicle, as shown in FIG.1B. Due to the multiple exhaust manifolds and different couplings of thescavenge manifold to the intake and exhaust passage, the split exhaustengine may include a unique air-fuel control system, as shown in FIGS.2A-2B. The scavenge exhaust valves and blowdown exhaust valves open andclose at different times in an engine cycle, for each cylinder, in orderto isolate scavenge and blowdown portions of combusted exhaust gases anddirect these portions separately to the scavenge manifold and blowdownmanifold, as shown at FIG. 3A. The timings of the intake valve, scavengeexhaust valve, and blowdown exhaust valve of each engine cylinder may beadjusted to increase EGR and/or blowthrough to the intake, and/oroptimize engine performance under different engine operating modes, asshown in FIG. 3B.

The positions of various valves and timings of the cylinder intake andexhaust valves of the split exhaust engine system may be controlleddifferently under different engine operating conditions, as shown atFIGS. 4A-4B. For example, the different operating modes of the splitexhaust engine system may include an electric mode (a method for thismode presented at FIG. 14 and corresponding, example timing graph shownat FIG. 23), a cold start mode (a method for this mode presented at FIG.5 and corresponding, example timing graph shown at FIG. 16), adeceleration fuel shut-off mode (a method for this mode presented atFIG. 6 and corresponding, example timing graph shown at FIG. 17), a partthrottle mode (a method for this mode presented at FIGS. 7A-7B andcorresponding, example timing graph shown at FIG. 18A-18B), an electricboost mode (a method for this mode presented at FIG. 8 andcorresponding, example timing graph shown at FIG. 19), a compressorthreshold mode (a method for this mode presented at FIG. 9 andcorresponding, example timing graph shown at FIG. 20), a shutdown mode(a method for this mode presented at FIG. 15 and corresponding, exampletiming graph shown at FIG. 24), and a baseline blowthrough combustioncooling (BTCC) mode (a method for this mode presented at FIGS. 10-13 andcorresponding, example timing graphs shown at FIGS. 21 and 22). During aperiod of operation of the engine (e.g., from a key-on startup tokey-off shutdown), the split exhaust engine system may transitionbetween multiple of the above-described operating modes. An example ofsuch a period of engine operation, from engine startup to shutdown, isshown at FIG. 25. In this way, engine actuators of the split exhaustengine system may be controlled differently based on a current operatingmode of the engine system in order to increase engine efficiency andreduce engine emissions at each engine operating mode.

In the following description, a valve being operational or activatedindicates that it is opened and/or closed according to determinedtimings during the combustion cycle for a given set of conditions.Likewise, a valve being deactivated or inoperative indicates that thevalve is maintained closed, unless otherwise stated.

FIG. 1A shows a schematic diagram of a multi-cylinder internalcombustion engine 10, which may be included in a propulsion system of anautomobile. Engine 10 includes a plurality of combustion chambers (i.e.,cylinders) which may be capped on the top by a cylinder head (notshown). In the example shown in FIG. 1A, engine 10 includes cylinders12, 14, 16, and 18, arranged in an inline-4 configuration. It should beunderstood, however, that though FIG. 1A shows four cylinders, engine 10may include any number of cylinders in any configuration, e.g., V-6,I-6, V-12, opposed 4, etc. Further, the cylinders shown in FIG. 1A mayhave a cylinder configuration, such as the cylinder configuration shownin FIG. 1B, as described further below. Each of cylinders 12, 14, 16,and 18 include two intake valves, including first intake valve 2 andsecond intake valve 4, and two exhaust valves, including first exhaustvalve (referred to herein as a blowdown exhaust valve, or blowdownvalve) 8 and second exhaust valve (referred to herein as a scavengeexhaust valve, or scavenge valve) 6. The intake valves and exhaustvalves may be referred to herein as cylinder intake valves and cylinderexhaust valves, respectively. As explained further below with referenceto FIG. 1B, a timing (e.g., opening timing, closing timing, openingduration, etc.) of each of the intake valves may be controlled viavarious camshaft timing systems. In one embodiment, both the firstintake valves 2 and second intake valves 4 may be controlled to a samevalve timing (e.g., such that they open and close at the same time inthe engine cycle). In an alternate embodiment, the first intake valves 2and second intake valves 4 may be controlled at a different valvetiming. Further, the first exhaust valves 8 may be controlled at adifferent valve timing than the second exhaust valves 6 (e.g., such thata first exhaust valve and second exhaust valve of a same cylinder openat different times than one another and close at different times thanone another), as discussed further below.

Each cylinder receives intake air (or a mixture of intake air andrecirculated exhaust gas, as explained further below) from an intakemanifold 44 via an air intake passage 28 Intake manifold 44 is coupledto the cylinders via intake ports (e.g., runners). For example, intakemanifold 44 is shown in FIG. 1A coupled to each first intake valve 2 ofeach cylinder via first intake ports 20. Further, the intake manifold 44is coupled to each second intake valve 4 of each cylinder via secondintake ports 22. In this way, each cylinder intake port can selectivelycommunicate with the cylinder it is coupled to via a corresponding oneof the first intake valves 2 or second intake valves 4. Each intake portmay supply air and/or fuel to the cylinder it is coupled to forcombustion.

One or more of the intake ports may include a charge motion controldevice, such as a charge motion control valve (CMCV). As shown in FIG.1A, each first intake port 20 of each cylinder includes a CMCV 24. CMCVs24 may also be referred to as swirl control valves or tumble controlvalves. CMCVs 24 may restrict airflow entering the cylinders via firstintake valves 2. In the example of FIG. 1A, each CMCV 24 may include avalve plate; however, other designs of the valve are possible. Note thatfor the purposes of this disclosure the CMCV 24 is in the “closed”position when it is fully activated and the valve plate may be fullytilted into the respective first intake port 20, thereby resulting inmaximum air charge flow obstruction. Alternatively, the CMCV 24 is inthe “open” position when deactivated and the valve plate may be fullyrotated to lie substantially parallel with airflow, thereby considerablyminimizing or eliminating airflow charge obstruction. The CMCVs mayprincipally be maintained in their “open” position and may only beactivated “closed” when swirl conditions are desired. As shown in FIG.1A, only one intake port of each cylinder includes the CMCV 24. However,in alternate embodiments, both intake ports of each cylinder may includea CMCV 24. The controller 12 may actuate the CMCVs 24 (e.g., via a valveactuator that may be coupled to a rotating shaft directly coupled toeach CMCV 24) to move the CMCVs into the open or closed positions, or aplurality of positions between the open and closed positions, inresponse to engine operating conditions (such as engine speed/loadand/or when blowthrough via the second exhaust valves 6 is active), asexplained further below. As referred to herein, blowthrough air orblowthrough combustion cooling may refer to intake air that flows fromthe one or more intake valves of each cylinder to second exhaust valves6 (and into second exhaust manifold 80) during a valve opening overlapperiod between the intake valves and second exhaust valves 6 (e.g., aperiod when both the intake valves and second exhaust valves 6 are openat the same time), without combusting the blowthrough air.

A high pressure, dual stage, fuel system (such as the fuel system shownin FIG. 1B) may be used to generate fuel pressures at injectors 66. Assuch, fuel may be directly injected in the cylinders via injectors 66.Distributorless ignition system 88 provides an ignition spark tocylinders 12, 14, 16, and 18 via sparks plug 92 in response tocontroller 12. Cylinders 12, 14, 16, and 18 are each coupled to twoexhaust ports for channeling the blowdown and scavenging portions of thecombustion gases separately. Specifically, as shown in FIG. 1A,cylinders 12, 14, 16, and 18 exhaust combustion gases (e.g., scavengingportion) to second exhaust manifold (referred to herein as a scavengemanifold) 80 via second exhaust runners (e.g., ports) 82 and combustiongases (e.g., blowdown portion) to first exhaust manifold (referred toherein as a blowdown manifold) 84 via first exhaust runners (e.g.,ports) 86. Second exhaust runners 82 extend from cylinders 12, 14, 16,and 18 to second exhaust manifold 80. Additionally, first exhaustmanifold 84 includes a first manifold portion 81 and second manifoldportion 85. First exhaust runners 86 of cylinders 12 and 18 (referred toherein as the outside cylinders) extend from cylinders 12 and 18 to thesecond manifold portion 85 of first exhaust manifold 84. Additionally,first exhaust runners 86 of cylinders 14 and 16 (referred to herein asthe inside cylinders) extend from cylinders 14 and 16 to the firstmanifold portion 81 of first exhaust manifold 84.

Each exhaust runner can selectively communicate with the cylinder it iscoupled to via an exhaust valve. For example, second exhaust runners 82communicate with their respective cylinders via second exhaust valves 6and first exhaust runners 86 communicate with their respective cylindersvia first exhaust valves 8. Second exhaust runners 82 are isolated fromfirst exhaust runners 86 when at least one exhaust valve of eachcylinder is in a closed position.

Exhaust gases may not flow directly between exhaust runners 82 and 86.The exhaust system described above may be referred to herein as a splitexhaust manifold system, where a first portion of exhaust gases fromeach cylinder are output to first exhaust manifold 84 and a secondportion of exhaust gases from each cylinder are output to second exhaustmanifold 80, and where the first and second exhaust manifolds do notdirectly communicate with one another (e.g., no passage directly couplesthe two exhaust manifolds to one another and thus the first and secondportions of exhaust gases do not mix with one another within the firstand second exhaust manifolds).

Engine 10 includes a turbocharger including a dual-stage exhaust turbine164 and an intake compressor 162 coupled on a common shaft. Dual-stageturbine 164 includes a first turbine 163 and second turbine 165. Firstturbine 163 is directly coupled to first manifold portion 81 of firstexhaust manifold 84 and receives exhaust gases only from cylinders 14and 16 via first exhaust valves 8 of cylinders 14 and 16. Second turbine165 is directly coupled to second manifold portion 85 of first exhaustmanifold 84 and receives exhaust gases only from cylinders 12 and 18 viafirst exhaust valves 8 of cylinders 12 and 18. Rotation of first andsecond turbines drives rotation of compressor 162 disposed within theintake passage 28. As such, the intake air becomes boosted (e.g.,pressurized) at the compressor 162 and travels downstream to intakemanifold 44. Exhaust gases exit both first turbine 163 and secondturbine 165 into common exhaust passage 74. A wastegate may be coupledacross the dual-stage turbine 164. Specifically, wastegate valve 76 maybe included in a bypass 78 coupled between each of the first manifoldportion 81 and second manifold portion 85, upstream of an inlet todual-stage turbine 164, and exhaust passage 74, downstream of an outletof dual-stage turbine 164. In this way, a position of wastegate valve(referred to herein as a turbine wastegate) 76 controls an amount ofboost provided by the turbocharger. In alternate embodiments, engine 10may include a single stage turbine where all exhaust gases from thefirst exhaust manifold 84 are directed to an inlet of a same turbine.

Exhaust gases exiting dual-stage turbine 164 flow downstream in exhaustpassage 74 to a first emission control device 70 and a second emissioncontrol device 72, second emission control device 72 arranged downstreamin exhaust passage 74 from first emission control device 70. Emissioncontrol devices 70 and 72 may include one or more catalyst bricks, inone example. In some examples, emission control devices 70 and 72 may bethree-way type catalysts. In other examples, emission control devices 70and 72 may include one or a plurality of a diesel oxidation catalyst(DOC), and a selective catalytic reduction catalyst (SCR). In yetanother example, second emission control device 72 may include agasoline particulate filter (GPF). In one example, first emissioncontrol device 70 may include a catalyst and second emission controldevice 72 may include a GPF. After passing through emission controldevices 70 and 72, exhaust gases may be directed out to a tailpipe.

Exhaust passage 74 further includes a plurality of exhaust sensors inelectronic communication with controller 12 of control system 15, asdescribed further below. As shown in FIG. 1A, exhaust passage 74includes a first oxygen sensor 90 positioned between first emissioncontrol device 70 and second emission control device 72. First oxygensensor 90 may be configured to measure an oxygen content of exhaust gasentering second emission control device 72. Exhaust passage 74 mayinclude one or more additional oxygen sensors positioned along exhaustpassage 74, such as second oxygen sensor 91 positioned betweendual-stage turbine 164 and first emission control device 70 and/or thirdoxygen sensor 93 positioned downstream of second emission control device72. As such, second oxygen sensor 91 may be configured to measure theoxygen content of the exhaust gas entering first emission control device70 and third oxygen sensor 93 may be configured to measure the oxygencontent of exhaust gas exiting second emission control device 72. In oneembodiment, the one or more oxygen sensor 90, 91, and 93 may beUniversal Exhaust Gas Oxygen (UEGO) sensors. Alternatively, a two-stateexhaust gas oxygen sensor may be substituted for oxygen sensors 90, 91,and 93. Exhaust passage 74 may include various other sensors, such asone or more temperature and/or pressure sensors. For example, as shownin FIG. 1A, a pressure sensor 96 is positioned within exhaust passage74, between first emission control device 70 and second emission controldevice 72. As such, pressure sensor 96 may be configured to measure thepressure of exhaust gas entering second emission control device 72. Bothpressure sensor 96 and oxygen sensor 90 are arranged within exhaustpassage 74 at a point where a flow passage 98 couples to exhaust passage74. Flow passage 98 may be referred to herein as a scavenge manifoldbypass passage (SMBP) 98. Scavenge manifold bypass passage 98 isdirectly coupled to and between second exhaust (e.g., scavenge) manifold80 and exhaust passage 74. A valve 97 (referred to herein as thescavenge manifold bypass valve, SMB V) is disposed within scavengemanifold bypass passage 98 and is actuatable by controller 12 to adjustan amount of exhaust flow from second exhaust manifold 80 to exhaustpassage 74, at a location between first emission control device 70 andsecond emission control device 72.

Second exhaust manifold 80 is directly coupled to a first exhaust gasrecirculation (EGR) passage 50. First EGR passage 50 is a coupleddirectly between second exhaust manifold 80 and intake passage 28,upstream of compressor (e.g., turbocharger compressor) 162 (and thus maybe referred to as a low-pressure EGR passage). As such, exhaust gases(or blowthrough air, as explained further below) is directed from secondexhaust manifold 80 to intake passage 28, upstream of compressor 162,via first EGR passage 50. As shown in FIG. 1A, first EGR passage 50includes an EGR cooler 52 configured to cool exhaust gases flowing fromsecond exhaust manifold 80 to intake passage 28 and a first EGR valve 54(which may be referred to herein as the BTCC valve). Controller 12 isconfigured to actuate and adjust a position of first EGR valve 54 inorder to control an amount of air flow through first EGR passage 50.When first EGR valve 54 is in a closed position, no exhaust gases orintake air may flow from second exhaust manifold 80 to intake passage28, upstream of compressor 162. Further, when first EGR valve 54 is inan open position, exhaust gases and/or blowthrough air may flow fromsecond exhaust manifold 80 to intake passage 28, upstream of compressor162. Controller 12 may additionally adjust first EGR valve 54 into aplurality of positions between fully open and fully closed.

A first ejector 56 is positioned at an outlet of EGR passage 50, withinintake passage 28. First ejector 56 may include a constriction orventuri that provides a pressure increase at the inlet of the compressor162. As a result, EGR from the EGR passage 50 may be mixed with freshair flowing through the intake passage 28 to the compressor 162. Thus,EGR from the EGR passage 50 may act as the motive flow on the firstejector 56. In an alternate embodiment, there may not be an ejectorpositioned at the outlet of EGR passage 50. Instead, an outlet ofcompressor 162 may be shaped as an ejector that lowers the gas pressureto assist in EGR flow (and thus, in this embodiment, air is the motiveflow and EGR is the secondary flow). In yet another embodiment, EGR fromEGR passage 50 may be introduced at the trailing edge of a blade ofcompressor 162, thereby allowing blowthrough air to intake passage 28via EGR passage 50.

A second EGR passage 58 is coupled between first EGR passage 50 andintake passage 28. Specifically, as shown in FIG. 1A, second EGR passage58 is coupled to first EGR passage 50, between EGR valve 54 and EGRcooler 52. In alternate embodiments, when second EGR passage 58 isincluded in the engine system, the system may not include EGR cooler 52.Additionally, second EGR passage 58 is directly coupled to intakepassage 28, downstream of compressor 162. Due to this coupling, secondEGR passage 58 may be referred to herein as a mid-pressure EGR passage.Further, as shown in FIG. 1A, second EGR passage 58 is coupled to intakepassage 28 upstream of a charge air cooler (CAC) 40. CAC 40 isconfigured to cool intake air (which may be a mixture of fresh intakeair from outside of the engine system and exhaust gases) as it passesthrough CAC 40. As such, recirculated exhaust gases from first EGRpassage 50 and/or second EGR passage 58 may be cooled via CAC 40 beforeentering intake manifold 44. In an alternate embodiment, second EGRpassage 58 may be coupled to intake passage 28, downstream of CAC 40. Inthis embodiment, there may be no EGR cooler 52 disposed within first EGRpassage 50. Further, as shown in FIG. 1A, a second ejector 57 may bepositioned within intake passage 28, at an outlet of second EGR passage58.

A second EGR valve 59 (e.g., mid-pressure EGR valve) is disposed withinsecond EGR passage 58. Second EGR valve 59 is configured to adjust anamount of gas flow (e.g., intake air or exhaust) through second EGRpassage 58. As described further below, controller 12 may actuate EGRvalve 59 into an open position (allowing flow thorough second EGRpassage 58), closed position (blocking flow through second EGR passage58), or plurality of positions between fully open and fully closed basedon (e.g., as a function of) engine operating conditions. For example,actuating the EGR valve 59 may include the controller 12 sending anelectronic signal to an actuator of the EGR valve 59 to move a valveplate of EGR valve 59 into an open position, closed position, or someposition between fully open and fully closed. As also explained furtherbelow, based on system pressures and positions of alternate valves inthe engine system, air may either flow toward intake passage 28 withinsecond EGR passage 58 or toward second exhaust manifold 80 within secondEGR passage 58.

Intake passage 28 further includes an electronic intake throttle 62 incommunication with intake manifold 44. As shown in FIG. 1A, intakethrottle 62 is positioned downstream of CAC 40. The position of athrottle plate 64 of throttle 62 can be adjusted by control system 15via a throttle actuator (not shown) communicatively coupled tocontroller 12. By modulating air intake throttle 62, while operatingcompressor 162, an amount of fresh air may be inducted from theatmosphere and/or an amount of recirculated exhaust gas from the one ormore EGR passages into engine 10, cooled by CAC 40 and delivered to theengine cylinders at compressor (or boosted) pressure via intake manifold44. To reduce compressor surge, at least a portion of the airchargecompressed by compressor 162 may be recirculated to the compressorinlet. A compressor recirculation passage 41 may be provided forrecirculating compressed air from the compressor outlet, upstream of CAC40, to the compressor inlet. Compressor recirculation valve (CRV) 42 maybe provided for adjusting an amount of recirculation flow recirculatedto the compressor inlet. In one example, CRV 42 may be actuated open viaa command from controller 12 in response to actual or expectedcompressor surge conditions.

A third flow passage 30 (which may be referred to herein as a hot pipe)is coupled between second exhaust manifold 80 and intake passage 28.Specifically, a first end of third flow passage 30 is directly coupledto second exhaust manifold 80 and a second end of third flow passage 30is directly coupled to intake passage 28, downstream of intake throttle62 and upstream of intake manifold 44. A third valve 32 (e.g., hot pipevalve) is disposed within third flow passage 30 and is configured toadjust an amount of air flow through third flow passage 30. Third valve32 may be actuated into a fully open position, fully closed position, ora plurality of positions between fully open and fully closed in responseto an actuation signal sent to an actuator of third valve 32 fromcontroller 12.

Second exhaust manifold 80 and/or second exhaust runners 82 may includeone or more sensors (such as pressure, oxygen, and/or temperaturesensors) disposed therein. For example, as shown in FIG. 1A, secondexhaust manifold 80 includes a pressure sensor 34 and oxygen sensor 36disposed therein and configured to measure a pressure and oxygencontent, respectively, of exhaust gases and blowthrough (e.g., intake)air, exiting second exhaust valves 6 and entering second exhaustmanifold 80. Additionally or alternatively to oxygen sensor 36, eachsecond exhaust runner 82 may include an individual oxygen sensor 38disposed therein. As such, an oxygen content of exhaust gases and/orblowthrough air exiting each cylinder via second exhaust valves 6 may bedetermined based on an output of oxygen sensors 38.

In some embodiments, as shown in FIG. 1A, intake passage 28 may includean electric compressor 60. Electric compressor 60 is disposed in abypass passage 61 which is coupled to intake passage 28, upstream anddownstream of an electric compressor valve 63. Specifically, an inlet tobypass passage 61 is coupled to intake passage 28 upstream of electriccompressor valve 63 and an outlet to bypass passage 61 is coupled tointake passage 28 downstream of electric compressor valve 63 andupstream of where first EGR passage 50 couples to intake passage 28.Further, the outlet of bypass passage 61 is coupled upstream in intakepassage 28 from turbocharger compressor 162. Electric compressor 60 maybe electrically driven by an electric motor using energy stored at anenergy storage device. In one example, the electric motor may be part ofelectric compressor 60, as shown in FIG. 1A. When additional boost(e.g., increased pressure of the intake air above atmospheric pressure)is requested, over an amount provided by compressor 162, controller 12may activate electric compressor 60 such that it rotates and increases apressure of intake air flowing through bypass passage 61. Further,controller 12 may actuate electric compressor valve 63 into a closed orpartially closed position to direct an increased amount of intake airthrough bypass passage 61 and electric compressor 60.

Intake passage 28 may include one or more additional sensors (such asadditional pressure, temperature, flow rate, and/or oxygen sensors). Forexample, as shown in FIG. 1A, intake passage 28 includes a mass air flow(MAF) sensor 48 disposed upstream of compressor 162, electric compressorvalve 63, and where first EGR passage 59 couples to intake passage 28.An intake pressure sensor 31 and intake temperature sensor 33 arepositioned in intake passage 28, upstream of compressor 162 anddownstream of where first EGR passage 50 couples to intake passage 28.An intake oxygen sensor 35 and an intake temperature sensor 43 may belocated in intake passage 28, downstream of compressor 162 and upstreamof CAC 40. An additional intake pressure sensor 37 may be positioned inintake passage 28, downstream of CAC 40 and upstream of throttle 28. Insome embodiments, as shown in FIG. 1A, an additional intake oxygensensor 39 may be positioned in intake passage 28, between CAC 40 andthrottle 28. Further, an intake manifold pressure (e.g., MAP) sensor 122and intake manifold temperature sensor 123 are positioned within intakemanifold 44, upstream of all engine cylinders.

In some examples, engine 10 may be coupled to an electric motor/batterysystem (as shown in FIG. 1B) in a hybrid vehicle. The hybrid vehicle mayhave a parallel configuration, series configuration, or variation orcombinations thereof. Further, in some embodiments, other engineconfigurations may be employed, for example a diesel engine.

Engine 10 may be controlled at least partially by a control system 15including controller 12 and by input from a vehicle operator via aninput device (not shown in FIG. 1A). Control system 15 is shownreceiving information from a plurality of sensors 16 (various examplesof which are described herein) and sending control signals to aplurality of actuators 81. As one example, sensors 16 may includepressure, temperature, and oxygen sensors located within the intakepassage 28, intake manifold 44, exhaust passage 74, and second exhaustmanifold 80, as described above. Other sensors may include a throttleinlet pressure (TIP) sensor for estimating a throttle inlet pressure(TIP) and/or a throttle inlet temperature sensor for estimating athrottle air temperature (TCT) coupled downstream of the throttle in theintake passage. Additional system sensors and actuators are elaboratedbelow with reference to FIG. 1B. As another example, actuators 81 mayinclude fuel injectors, valves 63, 42, 54, 59, 32, 97, 76, and throttle62. Actuators 81 may further includes various camshaft timing actuatorscoupled to the cylinder intake and exhaust valves (as described furtherbelow with reference to FIG. 1B). Controller 12 may receive input datafrom the various sensors, process the input data, and trigger theactuators in response to the processed input data based on instructionor code programmed in a memory of controller 12 corresponding to one ormore routines. Example control routines (e.g., methods) are describedherein at FIGS. 4-15. For example, adjusting EGR flow from secondexhaust manifold 80 to intake passage 28 may include adjusting anactuator of first EGR valve 54 to adjust an amount of exhaust flowflowing to intake passage 28, upstream of compressor 162, from secondexhaust manifold 80. In another example, adjusting EGR flow from secondexhaust manifold 80 to intake passage 28 may include adjusting anactuator of an exhaust valve camshaft to adjust an opening timing ofsecond exhaust valves 6.

In this way, the first and second exhaust manifolds of FIG. 1A may bedesigned to separately channel the blowdown and scavenging portions ofthe exhaust. First exhaust manifold 84 may channel the blowdown pulse ofthe exhaust to dual-stage turbine 164 via first manifold portion 81 andsecond manifold portion 85 while second exhaust manifold 80 may channelthe scavenging portion of exhaust to intake passage 28 via one or moreof first EGR passage 50 and second EGR passage 58 and/or to exhaustpassage 74, downstream of the dual-stage turbine 164, via flow passage98. For example, first exhaust valves 8 channel the blowdown portion ofthe exhaust gases through first exhaust manifold 84 to the dual-stageturbine 164 and both first and second emission control device 70 and 72while second exhaust valves 6 channel the scavenging portion of exhaustgases through second exhaust manifold 80 and to either intake passage 28via one or more EGR passages or exhaust passage 74 and second emissioncontrol device 72 via flow passage 98.

It should be noted that while FIG. 1A shows engine 10 including each offirst EGR passage 50, second EGR passage 58, flow passage 98, and flowpassage 30, in alternate embodiments, engine 10 may only include aportion of these passages. For example, in one embodiment, engine 10 mayonly include first EGR passage 50 and flow passage 98 and not includesecond EGR passage 58 and flow passage 30. In another embodiment, engine10 may include first EGR passage 50, second EGR passage 58, and flowpassage 98, but not include flow passage 30. In yet another embodiment,engine 10 may include first EGR passage 50, flow passage 30, and flowpassage 98, but not second EGR passage 58. In some embodiments, engine10 may not include electric compressor 60. In still other embodiments,engine 10 may include all or only a portion of the sensors shown in FIG.1A.

Referring now to FIG. 1B, it depicts a partial view of a single cylinderof internal combustion engine 10 which may be installed in a vehicle100. As such, components previously introduced in FIG. 1A arerepresented with the same reference numbers and are not re-introduced.Engine 10 is depicted with combustion chamber (cylinder) 130, coolantsleeve 114, and cylinder walls 132 with piston 136 positioned thereinand connected to crankshaft 140. Combustion chamber 130 is showncommunicating with intake passage 146 and exhaust passage 148 viarespective intake valve 152 and exhaust valve 156. As previouslydescribed in FIG. 1A, each cylinder of engine 10 may exhaust combustionproducts along two conduits. In the depicted view, exhaust passage 148represents the first exhaust runner (e.g., port) leading from thecylinder to the turbine (such as first exhaust runner 86 of FIG. 1A)while the second exhaust runner is not visible in this view.

As also previously elaborated in FIG. 1A, each cylinder of engine 10 mayinclude two intake valves and two exhaust valves. In the depicted view,intake valve 152 and exhaust valve 156 are located at an upper region ofcombustion chamber 130 Intake valve 152 and exhaust valve 156 may becontrolled by controller 12 using respective cam actuation systemsincluding one or more cams. The cam actuation systems may utilize one ormore of cam profile switching (CPS), variable cam timing (VCT), variablevalve timing (VVT) and/or variable valve lift (VVL) systems to varyvalve operation. In the depicted example, each intake valve 152 iscontrolled by an intake cam 151 and each exhaust valve 156 is controlledby an exhaust cam 153. The intake cam 151 may be actuated via an intakevalve timing actuator 101 and the exhaust cam 153 may be actuated via anexhaust valve timing actuator 103 according to set intake and exhaustvalve timings, respectively. In some examples, the intake valves andexhaust valves may be deactivated via the intake valve timing actuator101 and exhaust valve timing actuator 103, respectively. For example,the controller may send a signal to the exhaust valve timing actuator103 to deactivated the exhaust valve 156 such that it remains closed anddoes not open at its set timing. The position of intake valve 152 andexhaust valve 156 may be determined by valve position sensors 155 and157, respectively. As introduced above, in one example, all exhaustvalves of every cylinder may be controlled on a same exhaust camshaft Assuch, both a timing of the scavenge (second) exhaust valves and theblowdown (first) exhaust valves may be adjusted together via onecamshaft, but they may each have different timings relative to oneanother. In another example, the scavenge exhaust valve of everycylinder may be controlled on a first exhaust camshaft and a blowdownexhaust valve of every cylinder may be controlled on a different, secondexhaust camshaft. In this way, the valve timing of the scavenge valvesand blowdown valves may be adjusted separately from one another. Inalternate embodiments, the cam or valve timing system(s) of the scavengeand/or blowdown exhaust valves may employ a cam in cam system, anelectro-hydraulic type system on the scavenge valves, and/or anelectro-mechanical valve lift control on the scavenge valves.

For example, in some embodiments, the intake and/or exhaust valve may becontrolled by electric valve actuation. For example, cylinder 130 mayalternatively include an intake valve controlled via electric valveactuation and an exhaust valve controlled via cam actuation includingCPS and/or VCT systems. In still other embodiments, the intake andexhaust valves may be controlled by a common valve actuator or actuationsystem, or a variable valve timing actuator or actuation system.

In one example, intake cam 151 includes separate and different cam lobesthat provide different valve profiles (e.g., valve timing, valve lift,duration, etc.) for each of the two intake valves of combustion chamber130. Likewise, exhaust cam 153 may include separate and different camlobes that provide different valve profiles (e.g., valve timing, valvelift, duration, etc.) for each of the two exhaust valves of combustionchamber 130. In another example, intake cam 151 may include a commonlobe, or similar lobes, that provide a substantially similar valveprofile for each of the two intake valves.

In addition, different cam profiles for the different exhaust valves canbe used to separate exhaust gases exhausted at low cylinder pressurefrom exhaust gases exhausted at exhaust pressure. For example, a firstexhaust cam profile can open from closed position the first exhaustvalve (e.g., blowdown valve) just before BDC (bottom dead center) of thepower stroke of combustion chamber 130 and close the same exhaust valvewell before top dead center (TDC) to selectively exhaust blowdown gasesfrom the combustion chamber. Further, a second exhaust cam profile canbe positioned to open from close a second exhaust valve (e.g., scavengevalve) before a mid-point of the exhaust stroke and close it after TDCto selectively exhaust the scavenging portion of the exhaust gases.

Thus, the timing of the first exhaust valve and the second exhaust valvecan isolate cylinder blowdown gases from scavenging portion of exhaustgases while any residual exhaust gases in the clearance volume of thecylinder can be cleaned out with fresh intake air blowthrough duringpositive valve overlap between the intake valve and the scavenge exhaustvalves. By flowing a first portion of the exhaust gas leaving thecylinders (e.g., higher pressure exhaust) to the turbine(s) and a higherpressure exhaust passage and flowing a later, second portion of theexhaust gas (e.g., lower pressure exhaust) and blowthrough air to thecompressor inlet, the engine system efficiency is improved. Turbineenergy recovery may be enhanced and engine efficiency may be improvedvia increased EGR and reduced knock.

Continuing with FIG. 1B, exhaust gas sensor 126 is shown coupled toexhaust passage 148. Sensor 126 may be positioned in the exhaust passageupstream of one or more emission control devices, such as devices 70 and72 of FIG. 1A. Sensor 126 may be selected from among various suitablesensors for providing an indication of exhaust gas air/fuel ratio suchas a linear oxygen sensor or UEGO (universal or wide-range exhaust gasoxygen), a two-state oxygen sensor or EGO (as depicted), a HEGO (heatedEGO), a NOx, HC, or CO sensor, for example. The downstream emissioncontrol devices may include one or more of a three way catalyst (TWC),NOx trap, GPF, various other emission control devices, or combinationsthereof.

Exhaust temperature may be estimated by one or more temperature sensors(not shown) located in exhaust passage 148. Alternatively, exhausttemperature may be inferred based on engine operating conditions such asspeed, load, air-fuel ratio (AFR), spark retard, etc.

Cylinder 130 can have a compression ratio, which is the ratio of volumeswhen piston 136 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen, for example, when higher octane fuels orfuels with higher latent enthalpy of vaporization are used. Thecompression ratio may also be increased if direct injection is used dueto its effect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug92 for initiating combustion. Ignition system 188 can provide anignition spark to combustion chamber 130 via spark plug 92 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 92 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 130 is shown including one fuel injector 66. Fuelinjector 66 is shown coupled directly to combustion chamber 130 forinjecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12 via electronic driver 168. Inthis manner, fuel injector 66 provides what is known as direct injection(hereafter also referred to as “DI”) of fuel into combustion cylinder130. While FIG. 1B shows injector 66 as a side injector, it may also belocated overhead of the piston, such as near the position of spark plug92. Such a position may improve mixing and combustion when operating theengine with an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing. In an alternate embodiment,injector 66 may be a port injector providing fuel into the intake portupstream of cylinder 130.

Fuel may be delivered to fuel injector 66 from a high pressure fuelsystem 180 including fuel tanks, fuel pumps, and a fuel rail.Alternatively, fuel may be delivered by a single stage fuel pump atlower pressure, in which case the timing of the direct fuel injectionmay be more limited during the compression stroke than if a highpressure fuel system is used. Further, while not shown, the fuel tanksmay have a pressure transducer providing a signal to controller 12. Fueltanks in fuel system 180 may hold fuel with different fuel qualities,such as different fuel compositions. These differences may includedifferent alcohol content, different octane, different heat ofvaporizations, different fuel blends, and/or combinations thereof etc.In some embodiments, fuel system 180 may be coupled to a fuel vaporrecovery system including a canister for storing refueling and diurnalfuel vapors. The fuel vapors may be purged from the canister to theengine cylinders during engine operation when purge conditions are met.For example, the purge vapors may be naturally aspirated into thecylinder via the first intake passage at or below barometric pressure.

Engine 10 may be controlled at least partially by controller 12 and byinput from a vehicle operator 113 via an input device 118 such as anaccelerator pedal 116. The input device 118 sends a pedal positionsignal to controller 12. Controller 12 is shown in FIG. 1B as amicrocomputer, including a microprocessor unit 102, input/output ports104, an electronic storage medium for executable programs andcalibration values shown as a read only memory 106 in this particularexample, random access memory 108, keep alive memory 110, and a databus. Storage medium read-only memory 106 can be programmed with computerreadable data representing instructions executable by microprocessor 102for performing the methods and routines described below as well as othervariants that are anticipated but not specifically listed. Controller 12may receive various signals from sensors coupled to engine 10, inaddition to those signals previously discussed, including measurement ofinducted mass air flow (MAF) from mass air flow sensor 48; enginecoolant temperature (ECT) from temperature sensor 112 coupled to coolantsleeve 114; a profile ignition pickup signal (PIP) from Hall effectsensor 120 (or other type) coupled to crankshaft 140; throttle position(TP) from a throttle position sensor; absolute manifold pressure signal(MAP) from sensor 122, cylinder AFR from EGO sensor 126, and abnormalcombustion from a knock sensor and a crankshaft acceleration sensor.Engine speed signal, RPM, may be generated by controller 12 from signalPIP. Manifold pressure signal MAP from a manifold pressure sensor may beused to provide an indication of vacuum, or pressure, in the intakemanifold.

Based on input from one or more of the above-mentioned sensors,controller 12 may adjust one or more actuators, such as fuel injector66, throttle 62, spark plug 92, intake/exhaust valves and cams, etc. Thecontroller may receive input data from the various sensors, process theinput data, and trigger the actuators in response to the processed inputdata based on instruction or code programmed therein corresponding toone or more routines.

In some examples, vehicle 100 may be a hybrid vehicle with multiplesources of torque available to one or more vehicle wheels 160. In otherexamples, vehicle 100 is a conventional vehicle with only an engine, oran electric vehicle with only electric machine(s). In the example shownin FIG. 1B, vehicle 100 includes engine 10 and an electric machine 161.Electric machine 161 may be a motor or a motor/generator and thus mayalso be referred to herein as an electric motor. Crankshaft 140 ofengine 10 and electric machine 161 are connected via a transmission 167to vehicle wheels 160 when one or more clutches 166 are engaged. In thedepicted example, a first clutch 166 is provided between crankshaft 140and electric machine 161, and a second clutch 166 is provided betweenelectric machine 161 and transmission 167. Controller 12 may send asignal to an actuator of each clutch 166 to engage or disengage theclutch, so as to connect or disconnect crankshaft 140 from electricmachine 161 and the components connected thereto, and/or connect ordisconnect electric machine 161 from transmission 167 and the componentsconnected thereto. Transmission 167 may be a gearbox, a planetary gearsystem, or another type of transmission. The powertrain may beconfigured in various manners including as a parallel, a series, or aseries-parallel hybrid vehicle.

Electric machine 161 receives electrical power from a traction battery170 to provide torque to vehicle wheels 160. Electric machine 161 mayalso be operated as a generator to provide electrical power to chargebattery 170, for example during a braking operation.

Referring to FIG. 2A, a block diagram of an engine air-fuel ratiocontrol system 200 for an internal combustion engine 10 and an air-fuelratio flowing into an exhaust gas emissions device is shown. At leastportions of the system 200 may be incorporated into a system as shown inFIGS. 1A-1B as executable instructions stored in non-transitory memory.Other portions of system 200 may be actions performed via the controller12 shown in FIGS. 1A-1B to transform states of devices or actuators inthe real world. The engine air-fuel controller described herein may workin cooperation with sensors and actuators previously described.

A base desired engine air-fuel ratio is input at block 202. Block 202includes empirically determined air-fuel ratios for a plurality ofengine speed and load pairs. In one example, the empirically determinedair-fuel ratios are stored in a table in controller memory. The tablemay be indexed via present engine speed and engine load values. Thetable outputs a desired engine air-fuel ratio (e.g., 14.6:1) for thepresent engine speed and load. Block 202 outputs the desired engineair-fuel ratio to summing junction 204 and division junction 203.

An engine air mass flow as determined via a mass air flow sensor or anintake manifold pressure sensor (such as MAF 48 and/or MAP 122 shown inFIGS. 1A-1B) is input to control system 200 at block 201. The engine airmass flow is divided by the desired engine air-fuel ratio from block 202at division junction 203 to provide a desired engine fuel mass flowrate. The engine fuel mass flow rate is output to multiplicationjunction 208.

At summing junction 204, the actual engine air-fuel ratio as determinedfrom oxygen sensor 91 is subtracted from the desired engine air-fuelratio to provide an air-fuel ratio error. In addition, an air-fuel ratiobias or offset value is added to the desired engine air-fuel ratio andthe actual engine air-fuel ratio to improve catalyst efficiency. Theair-fuel ratio bias is output of summing junction 248. Summing junction204 outputs an air-fuel ratio error to proportional/integral controller206. Proportional/integral (PI) controller 206 integrates the error andapplies proportional and integral gains to the air-fuel ratio error tooutput a fuel flow control correction or adjustment to multiplicationjunction 208. The desired engine fuel mass flow rate from divisionjunction 203 is multiplied by the fuel flow control correction atmultiplication junction 208. The output of multiplication junction 208is an adjusted fuel flow amount that is converted to a fuel injectorpulse width at block 210 via a fuel injector transfer function. Block210 outputs a fuel pulse width to drive engine fuel injectors (e.g., notshown in FIG. 2A, shown in FIGS. 1A-1B as fuel injectors 66) and theengine fuel injectors inject the adjusted fuel flow amount or correctedfuel flow amount to engine 10.

The engine 10 outputs exhaust gases to turbocharger turbine (e.g.,163/165 from FIG. 1A). The exhaust gases pass through turbochargerturbine 163/165 and into emissions control device 70. Emissions controldevice 70 may be a three-way catalyst. Exhaust gases pass from emissionscontrol device 70 into emissions control device 72. Emissions controldevice 72 may be a three-way catalyst, a particulate filter, anoxidation catalyst, or a combination of catalyst and particulate filter.Processed exhaust gases flow to atmosphere after passing throughemissions control device 72. As explained above, the turbochargerturbine 163/165, emissions control device 70, and emissions controldevice 72 may be part of an exhaust system of the engine and may bepositioned along an exhaust passage of the engine.

Engine out exhaust gases may be sensed via oxygen sensor 91 to providean actual engine air-fuel ratio. The actual engine air-fuel ratio may beused as feedback in control system 200. The actual engine air-fuel ratiois input to summing junction 204. Exhaust gases downstream of emissionscontrol device 70 and upstream of emissions control device 72 may besampled via oxygen sensor 90 to determine an air-fuel ratio within theexhaust system. Oxygen sensor 90 is positioned in an exhaust passageextending between emissions control device 70 and emissions controldevice 72. Alternatively, exhaust gases may be sampled via an oxygensensor positioned downstream of emissions control device 72 (e.g.,oxygen sensor 93 shown in FIG. 1A) in place of oxygen sensor 90. Outputof oxygen sensor 90 or 93 is directed to switch 222 where it is thensent to summing junction 248 or to summing junction 232 based on thestate of switch 222 which is determined via mode switching logic 224.

Mode switching logic 224 determines an engine operating state and it maychange the position or state of switch 222 based on the engine operatingmode. In particular, mode switching logic commands switch 222 to itsbase position when engine air flow is less than a threshold and whenexhaust emissions devices are not requested to be regenerated. Modeswitching logic 224 also commands valve 97 of FIG. 1A positioned inscavenge manifold bypass passage 98 closed via first actuator referencefunction 226 when engine air flow is less than a threshold and whenexhaust emissions devices are not requested to be regenerated. Switch222 is shown in its base position. In its base or first position, switch222 sends oxygens sensor output data to summing junction 248. Air (e.g.,blowthrough) is not supplied to the exhaust system (via the scavengemanifold bypass passage 98) when switch 222 is in the first position.

Mode switching logic 224 moves switch 222 to a second position asindicated by arrow 250 as directed by mode switching logic 224 when theengine air flow amount is greater than a threshold or when an exhaustemissions device is to be regenerated. In its second position, switch222 directs output of oxygen sensor 90 to summing junction 232. Modeswitching logic 224 opens valve 97 via a control signal output fromfirst reference function 226 to valve 97 when the engine air flow amountis greater than a threshold or when an exhaust emissions device is to beregenerated. A rate of air flow provided to the exhaust system viascavenge manifold bypass passage 98 is open loop adjusted via secondreference function 228. In one example, second reference function 228outputs a valve position command, amount of intake and exhaust valveoverlap (e.g., a crankshaft angular duration where both the intake andexhaust valves are simultaneously open), a boost pressure command, orother air flow adjustment command that is based on the engine air-fuelratio and the mass flow rate of fuel and air combusted in the engine.For example, engine air-fuel ratio and mass flow rate of fuel and aircombusted in the engine may be used to index a table or function thatoutputs a valve position command, amount of intake valve and exhaustvalve overlap command, or boost pressure command The rate of air flowprovided to the exhaust system via the scavenge manifold is closed loopcontrolled via the air-fuel ratio input to summing junction 232. Valveopening amount, intake valve and exhaust valve overlap duration, boostpressure, or actuation of other actuators that may adjust air flowthrough scavenge manifold are adjusted at engine 10 according to thecontrol adjustments output from summing junction 236. Thus, PIcontroller 234 adjusts engine air flow actuators via modifying theoutput of the second reference function 228.

Alternatively, the rate of air flow provided to the exhaust system viathe scavenge manifold may be open loop controlled based on an estimateof soot mass stored in the emissions control device 72, or a temperatureestimate of emissions control device 72, instead of oxygen sensoroutput. The soot estimate may be based on a pressure differential acrossemissions control device 72 or other engine operating conditions asknown in the art. The temperature of emissions control device 72 may beestimated based on engine operating conditions such as engine speed andload. Further, the air flow rate may be closed loop controlled based ontemperature of emissions control device 72 or pressure differentialacross emissions control device 72. In such examples, temperature orpressure differential is substituted for the oxygen sensor input atsumming junction 232 and the air-fuel reference is replaced by atemperature or pressure reference. The air that flows to the exhaustsystem has not participated in combustion within the engine.

In one example, second reference function 228 outputs a control commandto a variable valve timing actuator (e.g., 101 and 103 shown in FIG. 1B)to adjust an amount of valve opening overlap between an intake valve andscavenge exhaust valve of a same cylinder and thus the blowthrough air(e.g., an amount of blowthrough air) directed to emissions controldevice 72. Alternatively, second reference function 228 outputs acontrol signal to a valve, such as valve 32 of FIG. 1A, or valve 97 ofFIG. 1A, each of which may adjust air flow to the exhaust system andemissions control device 72. Further, in some examples, second actuatorreference function 228 outputs a control signal to a turbochargerwastegate actuator used to adjust boost pressure, which also may beapplied to adjust air flow to emissions control device 72 via adjustingblowthrough air by raising and lowering boost pressure.

Timing of air delivery to the exhaust system from the scavenge manifoldmay be as follows: a stoichiometric or lean engine air-fuel ratio isrichened to a rich of stoichiometry engine air-fuel ratio and airsupplied to the exhaust system is delivered an engine cycle earlier tothe downstream emissions device 72 before exhaust gases produced fromthe rich of stoichiometry engine air-fuel ratio reach the location ofdownstream emissions device 72. The air delivery to the exhaust systemmay be ceased before leaning the rich or stoichiometry engine air-fuelratio.

When switch 222 is in its second position, oxygen sensor data fromoxygen sensor 90 or 93 is output to summing junction 232 instead ofsumming junction 248. An actual exhaust gas air-fuel ratio from oxygensensor 90 or 93 is subtracted from a desired exhaust gas air-fuel ratioprovided by reference block 230. The desired exhaust gas air-fuel ratiooutput from reference block 230 may be different from the desired engineair-fuel ratio output from block 202. In one example, the desiredexhaust gas air-fuel ratio is empirically determined and stored to atable that is indexed by engine speed and load. The desired exhaust gasair-fuel ratio output from block 230 may be a stoichiometric air-fuelratio when the engine air-fuel ratio is rich at high engine speeds andloads where engine air flow is greater than the threshold. The desiredexhaust air-fuel ratio output from block 230 may be lean ofstoichiometry when an exhaust emissions device is requested to beregenerated while the engine air-fuel ratio is stoichiometric.Subtracting the actual engine exhaust gas air-fuel ratio from thedesired engine exhaust gas air-fuel ratio provides an engine exhaust gasair-fuel ratio error that is input into a second PI controller 234. Theexhaust gas air-fuel ratio error is operated on by PI controller and acontrol correction is supplied to summing junction 236.

Engine speed (N) and load values are used to index air-fuel bias valuesin table 244. The air-fuel bias values are empirically determined valuesthat are stored in controller memory, and the air-fuel bias valuesprovide an adjustment to air-fuel mixtures in the exhaust system for thepurpose of improving catalyst efficiency. The air-fuel bias and theair-fuel ratio in the exhaust system are added to the desired engineair-fuel ratio and the engine output air-fuel ratio at summing junction204 when switch 222 is in its base position. If switch 222 is not in itsbase position, the output of summing junction 248 may be adjusted to apredetermined value, such as zero.

In a first example of how control system 200 may operate, the controladjustment output from summing junction 236 may be an adjustment for anamount of intake and exhaust valve overlap that results in air passingthrough the engine without having participated in combustion within theengine. By increasing intake and exhaust valve overlap, air flow throughthe engine and into the exhaust system via the scavenge manifold bypasspassage (e.g., 98 shown in FIG. 1A) may be increased. Conversely, bydecreasing intake and exhaust valve overlap, air flow through the engineand into the exhaust system via the scavenge manifold bypass passage maybe decreased.

In a second example of how control system 200 may operate, the controladjustment output from summing junction 236 may be an adjustment for thevalve (e.g., 97 of FIG. 1A) positioned in the scavenge manifold bypasspassage or a valve (e.g., 32 of FIG. 1A) positioned in a hot pipe (e.g.,30 of FIG. 1A). If engine 10 is operated at high loads using high boostpressure, intake manifold pressure may be greater than scavenge manifoldpressure and exhaust system pressure so that fresh air that has notparticipated in combustion may pass through the hot pipe to the scavengemanifold and into the exhaust system to lean exhaust gases and provideoxygen to emissions control device 72. Alternatively, fresh air may passthrough engine cylinders and into scavenge manifold 80 without havingparticipated in combustion. The air may then be directed to emissionscontrol device 72 via scavenge manifold bypass passage 98 to leanexhaust gases and provide oxygen to emissions control device 72. Air maybe directed to emissions control device 72 in the same ways in responseto a request to regenerate the emissions control device. In one examplewhere the emissions control device is a particulate filter, a request toregenerate the particulate filter may be made in response to a pressuredrop across the particulate filter exceeding a threshold pressure.

In this way, system 200 may control an engine air-fuel ratio observed byoxygen sensor 91 and an exhaust gas air-fuel ratio observed by oxygensensor 90 or 93 without directing air to the exhaust system in a firstmode. System 200 may also control an engine air-fuel ratio observed byoxygen sensor 91 and an exhaust gas air-fuel ratio observed by oxygensensor 90 or 93 when air is directed to the exhaust system via ascavenge manifold. The amount of air provided to the exhaust system thatdoes not participate in combustion within the engine may be closed loopfeedback controlled based on output from oxygen sensor 90 or 93 andadjustments to valves coupled to a scavenge manifold, intake and exhaustvalve overlap, or boost pressure.

Referring now to FIG. 2B, a block diagram of another embodiment of anengine air-fuel ratio control system 250 for an internal combustionengine 10 and an air-fuel ratio flowing into an exhaust gas emissionsdevice is shown. At least portions of the control system 250 may beincorporated into a system as shown in FIGS. 1A-1B as executableinstructions stored in non-transitory memory. Other portions of controlsystem 250 may be actions performed via the controller 12 shown in FIGS.1A-1B to transform states of devices or actuators in the real world. Theengine air-fuel controller described herein may work in cooperation withsensors and actuators previously described.

A base desired engine air-fuel ratio is input at block 252. Block 252includes empirically determined air-fuel ratios for a plurality ofengine speed and load pairs. In one example, the empirically determinedair-fuel ratios are stored in a table in controller memory. The tablemay be indexed via present engine speed and engine load values. Thetable outputs a desired engine air-fuel ratio (e.g., 14.6:1) for thepresent engine speed and load. Block 252 outputs the desired engineair-fuel ratio to summing junction 254 and division junction 253.

An engine air mass flow as determined via a mass air flow sensor or anintake manifold pressure sensor is input to control system 250 at block251. The engine air mass flow is divided by the desired engine air-fuelratio from block 252 at division junction 253 to provide a desiredengine fuel mass flow rate. The engine fuel mass flow rate is output tomultiplication junction 258.

At summing junction 254, the actual engine air-fuel ratio as determinedfrom oxygen sensor 91 is subtracted from the desired engine air-fuelratio to provide an air-fuel ratio error. In addition, an air-fuel ratiobias or offset value is added to the desired engine air-fuel ratio andthe actual engine air-fuel ratio to improve catalyst efficiency. Theair-fuel ratio bias is output of summing junction 278. Summing junction254 outputs an air-fuel ratio error to proportional/integral controller256. Proportional/integral (PI) controller 256 integrates the error andapplies proportional and integral gains to the air-fuel ratio error tooutput a fuel flow control correction or adjustment to multiplicationjunction 258. The desired engine fuel mass flow rate from divisionjunction 253 is multiplied by the fuel flow control correction atmultiplication junction 258. The output of multiplication junction 258is further adjusted at multiplication junction 259 in response to outputfrom PI controller 274. This adjustment compensates for variation in theexhaust gas air-fuel ratio within the exhaust system as determined viaoxygen sensor 90 or 93. The output of multiplication junction 259 (e.g.,a fuel flow adjustment) is converted to a fuel injector pulse width atblock 260 via a fuel injector transfer function. Block 260 outputs afuel pulse width to drive engine fuel injectors (e.g., not shown in FIG.2B, shown in FIGS. 1A-1B as items 66) and the engine fuel injectorsinject the adjusted fuel flow amount or corrected fuel flow amount toengine 10.

The engine 10 outputs exhaust gases to turbocharger turbine (e.g.,163/165 from FIG. 1A). The exhaust gases pass through turbochargerturbine 163/165 and into emissions control device 70. Emissions controldevice 70 may be a three-way catalyst. Exhaust gases pass from emissionscontrol device 70 into emissions control device 72. Emissions controldevice 72 may be a three-way catalyst, a particulate filter, anoxidation catalyst, or a combination of catalyst and particulate filter.Processed exhaust gases flow to atmosphere after passing throughemissions control device 72.

Engine out exhaust gases may be sensed via oxygen sensor 91 to providean actual engine air-fuel ratio. The actual engine air-fuel ratio may beused as feedback in control system 250. The actual engine air-fuel ratiois input to summing junction 254. Exhaust gases downstream of emissionscontrol device 70 and upstream of emissions control device 72 may besampled via oxygen sensor 90 to determine an air-fuel ratio within theexhaust system. Oxygen sensor 90 is positioned in an exhaust passageextending between emissions control device 70 and emissions controldevice 72. Alternatively, exhaust gases may be sampled via an oxygensensor positioned downstream of emissions control device 72 (e.g.,oxygen sensor 93 shown in FIG. 1A) in place of oxygen sensor 90. Outputof oxygen sensor 90 or 93 is directed to switch 262 where it is thensent to summing junction 278 or to summing junction 272 based on thestate of switch 262 which is determined via mode switching logic 264.

Mode switching logic 264 determines engine operating state and it maychange the position or state of switch 262 based on the engine operatingmode. In particular, mode switching logic commands switch 262 to itsbase position when engine air flow is less than a threshold and whenexhaust emissions devices are not requested to be regenerated. Modeswitching logic 264 also commands valve 97 of FIG. 1A positioned inscavenge manifold bypass passage 98 closed via first actuator referencefunction 266 when engine air flow is less than a threshold and whenexhaust emissions devices are not requested to be regenerated. Switch262 is shown in its base position. In its base or first position, switch262 sends oxygens sensor output data to summing junction 278.

Mode switching logic 264 moves switch 262 to a second position asindicated by arrow 150 as directed by mode switching logic 264 when theengine air flow amount is greater than a threshold or when an exhaustemissions device is to be regenerated. In its second position, switch262 directs output of oxygen sensor 90 to summing junction 272. Modeswitching logic 264 opens valve 97 via a control signal output fromfirst reference function 266 to valve 97 when the engine air flow amountis greater than a threshold or when an exhaust emissions device is to beregenerated. A rate of air flow provided to the exhaust system viascavenge manifold bypass passage 98 is open loop adjusted via secondreference function 268. In one example, second reference function 268outputs a valve position command, amount of intake and exhaust valveoverlap (e.g., a crankshaft angular duration where both the intake andexhaust valves are simultaneously open), a boost pressure command, orother air flow adjustment command that is based on the engine air-fuelratio and the mass flow rate of fuel and air combusted in the engine.For example, engine air-fuel ratio and mass flow rate of fuel and aircombusted in the engine may be used to index a table or function thatoutputs a valve position command, amount of intake valve and exhaustvalve overlap command, or boost pressure command.

Mode switching logic 264 may also control the path that air is directedto the exhaust system via the scavenge manifold bypass passage 98 inresponse to output of oxygen sensor 91, which is positioned in theexhaust system upstream of emissions control device 70. For example, ifoutput of oxygen sensor 91 is a first value (e.g., a first air-fuelratio estimate), air may be provided to the exhaust system at a locationupstream of emissions device 72 and downstream of emissions device 70via engine cylinders, the scavenge manifold, and the scavenge manifoldbypass pipe. The air flow rate supplied to the exhaust system may beadjusted via adjusting valve timing. If output of oxygen sensor 91 is asecond value (e.g., a second air-fuel ratio estimate), air may beprovided to the exhaust system at the location upstream of emissionsdevice 72 and downstream of emissions device 70 via the hot pipe 30, thescavenge manifold 80, and the scavenge manifold bypass pipe 98. The airflow rate supplied to the exhaust system may be adjusted via adjustingvalve 32 and or valve 97. By selectively routing air that has notparticipated in combustion through different paths, it may be possibleto deliver air to the exhaust system over a wider range of engineoperating conditions so that engine emissions may be reduced.

When switch 262 is in its second position, oxygen sensor data fromoxygen sensor 90 or 93 is output to summing junction 272 instead ofsumming junction 278. An actual exhaust gas air-fuel ratio from oxygensensor 90 or 93 is subtracted from a desired exhaust gas air-fuel ratioprovided by reference block 270. The desired exhaust gas air-fuel ratiooutput from reference block 270 may be different from the desired engineair-fuel ratio output from block 252. In one example, the desiredexhaust gas air-fuel ratio is empirically determined and stored to atable that is indexed by engine speed and load. The desired exhaust gasair-fuel ratio output from block 270 may be a stoichiometric air-fuelratio when the engine air-fuel ratio is rich at high engine speeds andloads. The desired exhaust air-fuel ratio output from block 270 may belean of stoichiometry when an exhaust emissions device is requested tobe regenerated while the engine air-fuel ratio is stoichiometric.Subtracting the actual engine exhaust gas air-fuel ratio from thedesired engine exhaust gas air-fuel ratio provides an engine exhaust gasair-fuel ratio error that is input into a second PI controller 274. Theexhaust gas air-fuel ratio error is operated on by PI controller 274,which integrates the air-fuel error and applies proportional andintegral gains to the output of summing junction 272, and a controlcorrection is supplied to multiplication junction 259.

Timing of air delivery to the exhaust system from the scavenge manifoldmay be as follows: a stoichiometric or lean engine air-fuel ratio isrichened to a rich of stoichiometry engine air-fuel ratio and airsupplied to the exhaust system is delivered an engine cycle or earlierto the downstream emissions device 72 before exhaust gases produced fromthe rich of stoichiometry engine air-fuel ratio reach the location ofdownstream emissions device 72. The air delivery to the exhaust systemmay be ceased before leaning the rich or stoichiometry engine air-fuelratio.

Engine speed (N) and load values are used to index air-fuel bias valuesin table 276. The air-fuel bias values are empirically determined valuesthat are stored in controller memory, and the air-fuel bias valuesprovide an adjustment to air-fuel mixtures in the exhaust system for thepurpose of improving catalyst efficiency. The air-fuel bias and theair-fuel ratio in the exhaust system are added to the desired engineair-fuel ratio and the engine output air-fuel ratio at summing junction254 when switch 262 is in its base position. If switch 262 is not in itsbase position, the output of summing junction 278 may be adjusted to apredetermined value, such as zero.

In this way, system 250 may control an engine air-fuel ratio observed byoxygen sensor 91 and an exhaust gas air-fuel ratio observed by oxygensensor 90 or 93 without directing air to the exhaust system in a firstmode. System 250 may also control an engine air-fuel ratio observed byoxygen sensor 91 and an exhaust gas air-fuel ratio observed by oxygensensor 90 or 93 when air is directed to the exhaust system via ascavenge manifold. An amount of fuel delivered to the engine may beclosed loop adjusted in response to an amount of air provided to theexhaust system that does not participate in combustion within theengine. The fuel injected to the engine may be adjusted based on outputfrom oxygen sensor 90 or 93.

As one example, a technical effect of supplying air to an exhaust systemat a location downstream of an emissions control device via a scavengemanifold, the air not having participated in combustion in an engine,the scavenge manifold in fluidic communication with a scavenge exhaustvalve of a cylinder and an intake manifold, the cylinder including ablowdown exhaust valve in fluidic communication with a blowdownmanifold; and adjusting an amount of fuel injected to the engine inresponse to output of a first oxygen sensor, the first oxygen sensorpositioned in the exhaust system upstream of the emissions controldevice, is more precisely controlling the air-fuel ratio of exhaustdownstream of the emissions control device for more efficient engineoperation and reduced engine emissions. As another example, a technicaleffect of flowing air from an intake manifold through a plurality ofengine cylinders to a junction of an exhaust passage and a bypasspassage in response to a condition, the junction positioned along theexhaust passage between first and second emission control devices; andflowing exhaust gas to the first emission control device while flowingthe air to the junction is increasing the amount of oxygen entering thesecond emission control device, thereby maintaining a stoichiometricmixture entering the second emission control device and thus, increasingfunction of the second emission control device and reducing engineemissions. In another example, this increased oxygen may help toregenerate and burn soot from the second emission control device andthus also result in increased function of the second emission controldevice and reduced emissions.

Now turning to FIG. 3A, graph 300 depicts example valve timings withrespect to a piston position, for an engine cylinder comprising 4valves: two intake valves and two exhaust valves, such as describedabove with reference to FIGS. 1A-1B. The example of FIG. 3A is drawnsubstantially to scale, even though each and every point is not labeledwith numerical values. As such, relative differences in timings can beestimated by the drawing dimensions. However, other relative timings maybe used, if desired.

Continuing with FIG. 3A, the cylinder is configured to receive intakevia two intake valves and exhaust a first blowdown portion to a turbineinlet via a first exhaust valve (e.g., such as first, or blowdown,exhaust valves 8 shown in FIG. 1A), exhaust a second scavenging portionto an intake passage via a second exhaust valve (e.g., such as second,or scavenge, exhaust valves 6 shown in FIG. 1A) and non-combustedblowthrough air to the intake passage via the second exhaust valve. Byadjusting the timing of the opening and/or closing of the second exhaustvalve with that of the two intake valves, residual exhaust gases in thecylinder clearance volume may be cleaned out and recirculated as EGRalong with fresh intake blowthrough air.

Graph 300 illustrates an engine position along the x-axis in crank angledegrees (CAD). Curve 302 depicts piston positions (along the y-axis),with reference to their location from top dead center (TDC) and/orbottom dead center (BDC), and further with reference to their locationwithin the four strokes (intake, compression, power and exhaust) of anengine cycle.

During engine operation, each cylinder typically undergoes a four strokecycle including an intake stroke, compression stroke, expansion stroke,and exhaust stroke. During the intake stroke, generally, the exhaustvalves close and intake valves open. Air is introduced into the cylindervia the corresponding intake passage, and the cylinder piston moves tothe bottom of the cylinder so as to increase the volume within thecylinder. The position at which the piston is near the bottom of thecylinder and at the end of its stroke (e.g. when the combustion chamberis at its largest volume) is typically referred to by those of skill inthe art as bottom dead center (BDC). During the compression stroke, theintake valves and exhaust valves are closed. The piston moves toward thecylinder head so as to compress the air within combustion chamber. Thepoint at which the piston is at the end of its stroke and closest to thecylinder head (e.g. when the combustion chamber is at its smallestvolume) is typically referred to by those of skill in the art as topdead center (TDC). In a process herein referred to as injection, fuel isintroduced into the combustion chamber. In a process herein referred toas ignition, the injected fuel is ignited by known ignition means, suchas a spark plug, resulting in combustion. During the expansion stroke,the expanding gases push the piston back to BDC. A crankshaft convertsthis piston movement into a rotational torque of the rotary shaft.During the exhaust stroke, in a traditional design, exhaust valves areopened to release the residual combusted air-fuel mixture to thecorresponding exhaust passages and the piston returns to TDC. In thisdescription, the second exhaust (scavenge) valves may be opened afterthe beginning of the exhaust stroke and stay open until after the end ofthe exhaust stroke while the first exhaust (blowdown) valves are closedand the intake valves are opened to flush out residual exhaust gaseswith blowthrough air.

Curve 304 depicts a first intake valve timing, lift, and duration for afirst intake valve (Int_1) while curve 306 depicts a second intake valvetiming, lift, and duration for a second intake valve (Int_2) coupled tothe intake passage of the engine cylinder. Curve 308 depicts an exampleexhaust valve timing, lift, and duration for a first exhaust valve(Exh_1, which may correspond to first, or blowdown, exhaust valves 8shown in FIG. 1A) coupled to a first exhaust manifold (e.g., blowdownexhaust manifold 84 shown in FIG. 1A) of the engine cylinder, whilecurve 310 depicts an example exhaust valve timing, lift, and durationfor a second exhaust valve (Exh_2, which may correspond to second, orscavenge, exhaust valves 6 shown in FIG. 1A) coupled to a second exhaustmanifold (e.g., scavenge manifold 80 shown in FIG. 1A) of the enginecylinder. As previously elaborated, the first exhaust manifold connectsa first exhaust valve to the inlet of a turbine in a turbocharger andthe second exhaust manifold connects a second exhaust valve to an intakepassage via an EGR passage. The first and second exhaust manifolds maybe separate from each other, as explained above.

In the depicted example, the first and second intake valves are fullyopened from a closed position at a common timing (curves 304 and 306),starting close to intake stroke TDC, just after CAD2 (e.g., at or justafter intake stroke TDC) and are closed after a subsequent compressionstroke has commenced past CAD3 (e.g., after BDC). Additionally, whenopened fully, the two intake valves may be opened with the same amountof valve lift L1 for the same duration of D1. In other examples, the twovalves may be operated with a different timing by adjusting the phasing,lift or duration based on engine conditions.

Now turning to the exhaust valves wherein the timing of the firstexhaust valve and the second exhaust valve is staggered relative to oneanother. Specifically, the first exhaust valve is opened from a closedposition at a first timing (curve 308) that is earlier in the enginecycle than the timing (curve 310) at which the second exhaust valve isopened from close. Specifically, the first timing for opening the firstexhaust valve is between TDC and BDC of the power stroke, before CAD1(e.g., before exhaust stroke BDC) while the timing for opening thesecond exhaust valve just after exhaust stroke BDC, after CAD1 butbefore CAD2. The first (curve 308) exhaust valve is closed before theend of the exhaust stroke and the second (curve 310) exhaust valve isclosed after the end of the exhaust stroke. Thus, the second exhaustvalve remains open to overlap slightly with opening of the intakevalves.

To elaborate, the first exhaust valve may be fully opened from closebefore the start of an exhaust stroke (e.g., between 90 and 40 degreesbefore BDC), maintained fully open through a first part of the exhauststroke and may be fully closed before the exhaust stroke ends (e.g.,between 50 and 0 degrees before TDC) to collect the blowdown portion ofthe exhaust pulse. The second exhaust valve (curve 310) may be fullyopened from a closed position just after the beginning of the exhauststroke (e.g., between 40 and 90 degrees past BDC), maintained openthrough a second portion of the exhaust stroke and may be fully closedafter the intake stroke begins (e.g., between 20 and 70 degrees afterTDC) to exhaust the scavenging portion of the exhaust. Additionally, thesecond exhaust valve and the intake valves, as shown in FIG. 3A, mayhave a positive overlap phase (e.g., from between 20 degrees before TDCand 40 degrees after TDC until between 40 and 90 degrees past TDC) toallow blowthrough with EGR. This cycle, wherein all four valves areoperational, may repeat itself based on engine operating conditions.

Additionally, the first exhaust valve may be opened at a first timingwith a first amount of valve lift L2 while the second exhaust valve maybe opened with a second amount of valve lift L3 (curve 310), where L3 issmaller than L2. Further still, the first exhaust valve may be opened atthe first timing for a duration D2 while the second exhaust valve may beopened for a duration D3, where D3 is smaller than D2. It will beappreciated that in alternate embodiments, the two exhaust valves mayhave the same amount of valve lift and/or same duration of opening whileopening at differently phased timings.

In this way, by using staggered valve timings, engine efficiency andpower can be increased by separating exhaust gases released at higherpressure (e.g., expanding blow-down exhaust gases in a cylinder) fromresidual exhaust gases at low pressure (e.g., exhaust gases that remainin the cylinder after blow-down) into the different passages. Byconveying low pressure residual exhaust gases as EGR along withblowthrough air to the compressor inlet (via the EGR passage and secondexhaust manifold), combustion chamber temperatures can be lowered,thereby reducing knock and spark retard from maximum torque. Further,since the exhaust gases at the end of the stroke are directed to eitherdownstream of a turbine or upstream of a compressor which are both atlower pressures, exhaust pumping losses can be minimized to improveengine efficiency.

Thus, exhaust gases can be used more efficiently than simply directingall the exhaust gas of a cylinder through a single, common exhaust portto a turbocharger turbine. As such, several advantages may be achieved.For example, the average exhaust gas pressure supplied to theturbocharger can be increased by separating and directing the blowdownpulse into the turbine inlet to improve turbocharger output.Additionally, fuel economy may be improved because blowthrough air isnot routed to the catalyst, being directed to the compressor inletinstead, and therefore, excess fuel may not be injected into the exhaustgases to maintain a stoichiometric ratio.

FIG. 3A may represent base intake and exhaust valve timing settings forthe engine system. Under different engine operating modes, the intakeand exhaust valve timing may be adjusted from the base settings. FIG. 3Bshows example adjustments to the valve timings of the blowdown exhaustvalve (BDV), scavenge exhaust valve (SV), and intake valve (IV) for arepresentative cylinder at different engine operating modes.Specifically, graph 320 illustrates an engine position along the x-axisin crank angle degrees (CAD). Graph 320 also illustrates changes to thetiming of the BDV, IV, and SV of each cylinder for a baselineblowthrough combustion cooling (BTCC) mode with higher EGR at plot 322,a baseline BTCC mode with lower EGR at plot 324, a first cold start mode(A) at plot 326, a second cold start mode (B) at plot 328, adeceleration fuel shut-off (DFSO) mode at plot 330, a BTCC mode in anengine system without a scavenge manifold bypass passage (e.g., passage98 shown in FIG. 1A), an early intake valve closing (EIVC) mode at plot334, and a compressor threshold mode at plot 336. In the examples showin FIG. 3B, it is assumed that the SVs and BDVs move together (e.g., viaa same cam of a cam timing system). In this way, though the SVs and BDVsmay open and close at different timings relative to one another, theymay be adjusted (e.g., advanced or retarded) together, by a same amount.However, in alternate embodiments, the BDVs and SVs may be controlledseparately and thus may be adjustable separately from one another.

During the baseline BTCC mode with higher EGR, as shown at plot 322, thevalve timings may be at their base settings. The SV and BDV are at fulladvance (e.g., as advanced as the valve timing hardware allows). In thismode, blowthrough to the intake via the SV may be increased by retardingthe SV and/or advancing the IV (increases IV and SV overlap and thusblowthrough). By retarding the BDV and SV, EGR decreases, as shown atplot 324 in the baseline BTCC mode with lower EGR. As seen at plot 326,during the first cold start mode (A), the SV may be adjusted to an earlyopen/high lift profile. During a second cold start mode (B), as shown atplot 328, the SV may be deactivated such that it does not open. Further,the IV may be advanced while the BDV is retarded, thereby increasingcombustion stability.

During the DFSO mode, at plot 330, the BDV may be deactivated (e.g.,such that it is maintained closed and does not open at its set timing).The IV and SV timings may maintain at their base position, or the SV maybe retarded to increase overlap between the SV and IV, as shown at plot330. As a result, all the combusted exhaust gases are exhausted to thescavenge exhaust manifold via the SV and routed back to the intakepassage. Plot 334 shows the EIVC mode where the IV is deactivated andthe exhaust cam is phased to the max retard. Thus, the SV and BDV areretarded together. As described further below with reference to FIG. 7A,this mode allows for air to be inducted into the engine cylinder via theSV and exhausted via the BDV. Plot 336 shows an example valve timing fora compressor threshold mode. In this mode, the intake cam of the IV isadvanced and the exhaust cam of the SV and BDV is retarded to decreaseEGR and reduce exhaust flow to the inlet of the compressor. More detailson these operating modes will be discussed below with reference to FIGS.4-15.

Now turning to FIGS. 4A-4B, a flow chart of a method 400 for operating avehicle including a split exhaust engine system (such as the systemshown in FIGS. 1A-1B), where a first exhaust manifold (e.g., scavengemanifold 80 shown in FIG. 1A) routes exhaust gas and blowthrough air toan intake of the engine system and a second exhaust manifold (e.g.,blowdown manifold 84 shown in FIG. 1A) routes exhaust to an exhaust ofthe engine system, under different vehicle and engine operating modes isshown. Instructions for carrying out method 400 and the rest of themethods included herein may be executed by a controller (such ascontroller 12 shown in FIGS. 1A-1B) based on instructions stored on amemory of the controller and in conjunction with signals received fromsensors of the engine system, such as the sensors described above withreference to FIG. 1A-1B. The controller may employ engine actuators ofthe engine system to adjust engine operation, according to the methodsdescribed below. For example, the controller may actuate various valveactuators of various valves to move the valves into commanded positionsand/or actuate various valve timing actuators of various cylinder valvesto adjust the timing of the cylinder valves.

Method 400 begins at 402 by estimating and/or measuring vehicle andengine operating conditions. Engine operating conditions may include abrake pedal position, acceleration pedal position, operator torquedemand, battery state of charge (in a hybrid electric vehicle), ambienttemperature and humidity, barometric pressure, engine speed, engineload, an amount of input to a transmission of a vehicle in which theengine is installed from an electric machine (e.g., electric machine 161shown in FIG. 1B) or crankshaft of the engine, engine temperature, massair flow (MAF), intake manifold pressure (MAP), oxygen content of intakeair/exhaust gases at various points in the engine system, a timing ofthe cylinder intake and exhaust valves, positions of various valves ofthe engine system, a temperature and/or loading level of one or moreemission control devices, pressures in the exhaust manifolds, exhaustrunners, exhaust passage and/or intake passage, an amount of fuel beinginjected into engine cylinders, an operation state of an electriccompressor (e.g., electric compressor 60 shown in FIG. 1A), a speed ofthe turbocharger, condensate formation at the turbocharger compressor, atemperature at the turbocharger compressor inlet and/or outlet, etc.

At 403, the method includes determining if the vehicle is operating inan electric mode. As explained above, in one embodiment, the vehicle maybe a hybrid electric vehicle. A vehicle mode of operation may bedetermined based on the estimated operating conditions. For example,based at least on the estimated driver torque demand and the batterystate of charge, it may be determined whether the vehicle is to beoperated in an engine-only mode (with the engine driving the vehiclewheels), an assist mode (with the battery assisting the engine indriving the vehicle), or an electric-only mode (with only the batterydriving the vehicle via an electric motor or generator). In one example,if the demanded torque can be provided by only the battery, the vehiclemay be operated in the electric-only mode with the vehicle beingpropelled using motor torque only. In another example, if the demandedtorque cannot be provided by the battery, the vehicle may be operated inthe engine mode, or in the assist mode where the vehicle is propelledwith at least some engine torque. The vehicle may accordingly beoperated in the determined mode of operation. If it is confirmed at 403that the vehicle is operating in the electric-only mode, the methodcontinues to 405 to operate in the electric-only (e.g., electric) modewhich includes propelling the hybrid vehicle via only motor torque (andnot engine torque). Details on operating in the electric mode arediscussed further below with reference to FIG. 14.

Alternatively, if the vehicle is not operating in the electric mode, orthe vehicle is not a hybrid vehicle, the vehicle may be propelled withat least some (or all) engine torque and proceed to 404. At 404, themethod includes determining if cold start conditions are met. In oneexample, a cold start condition may include the engine operating with anengine temperature below a threshold temperature. In one example, theengine temperature may be a coolant temperature. In another example, theengine temperature may be a temperature of a catalyst (e.g., of anemission control device, such as one of emission control devises 70 and72 shown in FIG. 1A) positioned in the exhaust passage. If the engine isoperating under the cold start condition, the method continues to 406 tooperate in a cold start mode. Details on operating in the cold startmode are discussed further below with reference to FIG. 5.

Otherwise, if cold start conditions are not met (e.g., enginetemperatures are above set thresholds), the method continues to 408. At408, the method include determining whether a deceleration fuel shut-off(DFSO) event is occurring (or whether the vehicle is decelerating). Asone example, a DFSO event may be initiated and/or indicated when anoperator releases an accelerator pedal of the vehicle and/or depresses abrake pedal. In another example, a DFSO event may be indicated whenvehicle speed decreases by a threshold amount. The DFSO event mayinclude stopping fuel injection into the engine cylinders. If the DFSOevent is occurring, the method continues to 410 to operate in a DFSOmode. Details on operating in the DFSO mode are discussed further belowwith reference to FIG. 6.

If DFSO conditions are not met or DFSO is not occurring, the methodcontinues to 412. At 412, the method includes determining if engine loadis below a threshold load. In one example, the threshold load may be alower threshold load at which a part throttle condition (e.g., when anintake throttle, such as throttle 62 shown in FIG. 1A is at leastpartially closed, such that it is not fully open) occurs and/or at whichan engine idle condition (e.g., when the engine is idling) occurs. Insome examples, the threshold load may be based on a load and/or throttleopening at which reverse flow may occur through the EGR passage (e.g.,passage 50 shown in FIG. 1A) and scavenge exhaust manifold. Reverse flowmay include intake air flowing from the intake passage, through the EGRpassage and scavenge exhaust manifold and into the engine cylinders viathe scavenge exhaust valves. If the engine load is below the thresholdload (or the throttle is not fully open and thus at least partiallyclosed), the method continues to 414 to operate in a part throttle mode.Details on operating in the part throttle mode are discussed furtherbelow with reference to FIGS. 7A-7B.

If engine load is not below the threshold load at 412, the methodcontinues to 416. At 416, the method includes determining if an electriccompressor in the engine system is operating. In one example, theelectric compressor may be an electric compressor positioned in theintake passage, upstream of where the EGR passage (coupled to thescavenge manifold) couples to the intake passage and upstream of theturbocharger compressor (such as electric compressor 60 shown in FIG.1A). As one example, the controller may determine that the electriccompressor is operating when the electric compressor is beingelectrically driven by energy stored at an energy storage device (suchas a battery). For example, an electric motor (coupled to the energystorage device) may drive the electric compressor and thus, when theelectric motor is operating and driving the electric compressor, thecontroller may determine that the electric compressor is operating. Theelectric compressor may be turned on and driven by the motor and storedenergy in response to a request for additional boost (e.g., a pressureamount above that which may be provided via the turbocharger compressoralone at a current turbocharger speed). If the electric compressor isbeing driven by the electric motor of the electric compressor, and thusoperated, at 416, the method continues to 418 to operate in the electricboost mode. Details on operating in the electric boost mode arediscussed further below with reference to FIG. 8.

If the electric compressor is not operating (e.g., not being driven byan electric motor coupled with the electric compressor), the methodcontinues to 420. At 420, the method includes determining whether thecompressor (e.g., turbocharger compressor 162 shown in FIG. 1A) is at anoperational threshold. The operational threshold (e.g., limit) of thecompressor may include one or more of an inlet temperature of thecompressor being less than a first threshold temperature (which may beindicative of condensate forming at the compressor inlet), an outlettemperature of the compressor being greater than a second thresholdtemperature (where temperatures at or above this second thresholdtemperature may result in degradation of the compressor), and/or arotational speed of the compressor (e.g., compressor speed which is alsothe turbocharger speed) being greater than a threshold speed (wherespeeds above this threshold may result in degradation of thecompressor). When the compressor is operating above these operationalthresholds, compressor degradation and/or reduced performance may occur.In another example, the method at 420 may additionally or alternativelyinclude determining whether engine speed (RPM) or engine load are aboverespective thresholds. For example, the engine speed and/or loadthresholds may be correlated to compressor operation such that when theengine is operating at these engine speed or engine load thresholds, thecompressor may reach one or more of the above described operationalthresholds. As such, at relatively high engine power, speed, and/orload, the compressor may reach one or more of the operationalthresholds. If the compressor is at or above one of the operationalthresholds, or the engine speed and/or load are at their respectiveupper thresholds, the method continues to 421 to operate in thecompressor threshold mode (which may also be referred to herein as thehigh power mode). Details on operating in the compressor threshold modeare discussed further below with reference to FIG. 9.

If the compressor is not operating at one of the operational thresholds(or engine speed and/or load are below their upper thresholds), themethod continues to 422. At 422, the method includes determining whetherthere is a low RPM transient tip-in condition. As one example, the lowRPM transient tip-in condition may include when there is an increase intorque demand above a threshold torque demand while engine speed isbelow a threshold speed. For example, if a pedal position signal from anaccelerator pedal is greater than a threshold (indicating that theaccelerator pedal has been depressed by a threshold amount, therebyindicating a requested increase in torque output of the engine) whileengine speed is below the threshold speed, the controller may determinethat there is a low RPM transient tip-in condition. If it is determinedthat the conditions for the low RPM transient tip-in are met, the methodcontinues to 423 to decrease the amount of opening of the BTCC valve(e.g., valve 54 shown in FIG. 1A) to increase the scavenge manifoldpressure to a desired level, where the desired level is based on intakemanifold pressure (MAP) and the variable cam timing (VCT) of the intakeand exhaust valves. For example, the method at 423 may include thecontroller determining the desired scavenge manifold pressure based onan estimated or measured MAP and the current timings (e.g., opening andclosing timings) of the intake and exhaust (e.g., scavenge and blowdown)valves. For example, when the BTCC valve is fully open, the scavengemanifold operates close to the compressor inlet pressure (e.g., ambientpressure). In this mode, EGR and blowthrough are higher, thereby leadingto higher engine efficiency but little excess reserve throttling.Raising the desired (e.g., target) scavenge manifold pressure closer toMAP may decrease the EGR and blowthrough so more charge air is trappedin the cylinders. Thus, by using feedback on the pressure in thescavenge manifold, the BTCC valve can be modulated to reach the desiredlevel of EGR. For example, the target scavenge manifold pressure for agiven level of output torque may be mapped (e.g., in a table or mapstored in the memory of the controller) vs. intake/exhaust valve VCT. Inthis way, the controller may use a stored relationship of scavengemanifold pressure vs. intake/exhaust valve VCT.

As one example, the controller may use a first look-up table stored inmemory to determine the desired scavenge manifold pressure, with MAP andthe intake and exhaust valve timings as the inputs and the desiredscavenge manifold pressure as the output. The controller may then use asecond look-up table, with the determined desired scavenge manifoldpressure as the input and one or more of a desired BTCC valve position,a duration of fully closing the BTCC valve, or an amount of decreasingthe amount of opening the BTCC valve as the output, to determine thecommanded BTCC valve position. The controller may then send a signal toan actuator of the BTCC valve to move the BTCC valve into the desiredposition (e.g., fully closed or partially closed) and hold the BTCCvalve in that position for the determined duration. As another example,the controller may make a logical determination (e.g., regarding aposition of the BTCC valve) based on logic rules that are a function ofMAP, intake valve timing, and exhaust valve timing. The controller maythen generate a control signal that is sent to the actuator of the BTCCvalve. In some embodiments, the method at 423 may include closing theBTCC valve until the desired scavenge manifold pressure is reached andthen reopening the BTCC valve. In another example, the method at 423 mayinclude modulating the BTCC valve between open and closed positions tomaintain the scavenge manifold pressure at the desired pressure. Thescavenge manifold pressure may be measured via one or more pressuresensors positioned in the scavenge manifold or exhaust runners of thescavenge exhaust valves and then the measured scavenge manifold pressuremay be used, by the controller, as feedback to further adjust theposition of the BTCC valve to maintain the scavenge manifold at thedesired scavenge manifold pressure. In some examples, the controller mayuse another look-up table with the measured scavenge manifold pressureand desired scavenged manifold pressures as inputs and an adjusted BTCCvalve position as the output.

If there is not a low RPM transient tip-in condition at 422, the methodinstead continues to 424 of FIG. 4B. At 424, the method includesdetermining if an engine shutdown is expected or requested. The engineshutdown may include a key off shutdown (e.g., when the vehicle is putin park and an operator turns off the engine) or a start/stop shutdown(e.g., when the vehicle is stopped but not parked and the engineautomatically shuts down responsive to stopping for a thresholdduration). Thus, in one example, the controller may determine that ashutdown is requested in response to receiving a key off signal from anignition of the vehicle and/or the vehicle being stopped for a thresholdduration. If a shutdown request is received at the controller, themethod continues to 426 to operate in a shutdown mode. Details onoperating in the shutdown mode are discussed further below withreference to FIG. 15.

If a shutdown request is not received at 424, the method continues to428. At 428, the method includes determining if blowthrough combustioncooling (BTCC) and EGR to the intake passage via the scavenge exhaustmanifold (e.g., via scavenge manifold 80 and first EGR passage 50 shownin FIG. 1A) is desired or currently enabled. For example, if engine loadis above a second threshold load (e.g., higher than the threshold loadat 412), blowthrough and EGR to the intake passage may be desired andenabled. In another example, if the BTCC hardware of the engine (e.g.,the BTCC valve 54 and/or scavenge exhaust valves 6 shown in FIG. 1A) isactivated, then blowthrough and EGR may be enabled. For example, it maybe determined that the BTCC hardware is activated if the scavengeexhaust valves are operating (e.g., not deactivated) and the BTCC valveis open or at least partially open. If blowthrough and EGR are desiredand/or the BTCC hardware is already activated, the method continues to430 to operate in the baseline BTCC mode. Details on operating in thebaseline BTCC mode are described further below with reference to FIGS.10-13.

Alternatively at 428, if BTCC is not desired, the method continues to432 to deactivate the scavenge exhaust valves and operate the enginewithout blowthrough. For example, this may include maintaining thescavenge exhaust valves closed and routing exhaust gases from the enginecylinders to only the exhaust passage via the blowdown exhaust valves.As one example, the controller may send a deactivation signal to thevalve actuators of the scavenge valves (e.g., exhaust valve timingactuator 103 shown in FIG. 1A) to deactivate the SVs of every cylinder.Further, the method at 431 may include not operating the engine withEGR. The method then continues to 434 to maintain the charge motioncontrol valves (e.g., CMCVs 24 shown in FIG. 1A) open so no intake airis blocked when entering the engine cylinders via the intake runners.The method then ends.

Turning now to FIG. 5, a method 500 for operating the engine system in acold start mode is shown. Method 500 may continue from 406 of method400, as described above. Method 500 begins at 502 by determining if thescavenge exhaust valves (e.g., second exhaust valves 6 shown in FIG. 1A)are default activated. The scavenge exhaust valves (SVs) may be defaultactivated (e.g., opened) if the valve actuation mechanism (e.g., such asvarious valve lift and/or VCT mechanisms, as described above and shownas exhaust valve timing actuator 103 in FIG. 1B) of the scavenge exhaustvalves is activated so that the scavenge exhaust valves will be actuatedto open at their set timing. In some examples, the valve actuationmechanism may be deactivated so that the scavenge exhaust valves willnot open (and instead remain closed) at their set timing in the enginecycle. The default setting may be the activation state of the scavengeexhaust valves at engine shutdown. In this way, the scavenge exhaustvalves may either be default activated or deactivated upon enginestartup and during the cold start. If the scavenge exhaust valves aredefault activated, the method continues to 504 to open the BTCC valve(e.g., valve 54 shown in FIG. 1A) for the initial crank (e.g., initialrotation of the crankshaft)

At 506, the method includes, after firing the first cylinder (e.g.,after injecting fuel into and combusting the air and fuel within thefirst cylinder), modulating a position of the BTCC valve to control EGRthrough the EGR passage (e.g., passage 50 shown in FIG. 1A) and to theinlet of the compressor to a desired EGR flow amount. The desired EGRflow amount may be set based on engine operating conditions (e.g., suchas engine load, MAF, combustion A/F, and/or set emissions thresholds).In one example, modulating the position of the BTCC valve may includeswitching the position of the BTCC valve between a fully open and fullyclosed position to maintain a desired EGR flow rate to the intakepassage, upstream of the compressor. In an alternate example, where theBTCC valve is a continuously variable valve adjustable into more thantwo positions, modulating the position of the BTCC valve may includecontinuously adjusting the position of the BTCC valve into a pluralityof positions between fully open and fully closed to maintain the desiredEGR flow rate. Further, the method at 506 may include adjusting theposition of the BTCC valve to prevent reverse flow through the EGRpassage (e.g., intake air flow through the EGR passage from the intakepassage to the scavenge exhaust manifold). For example, in response to apressure of the scavenge exhaust manifold (e.g., second exhaust manifold80 shown in FIG. 1A) being less than atmospheric pressure, thecontroller may actuate the BTCC valve into the fully closed position toblock flow through the EGR passage. Thus, in some examples, the methodat 506 may include the controller making a logical determination (e.g.,regarding a position of the BTCC valve) based on logic rules that are afunction of desired EGR flow and a pressure in the scavenge exhaustvalve. As another example, the controller may include a look-up tablestored in memory with desired EGR flow and scavenge manifold pressure asinputs and the BTCC valve position as the output. The controller maythen generate a control signal that is sent to an actuator of the BTCCvalve and results in adjusting the BTCC valve (e.g., adjusting a valveplate of the BTCC valve) into the determined position. If the BTCC valveis closed at 506, the method may further include, opening (or at leastpartially opening) the scavenge manifold bypass valve (e.g., in anengine system that includes a scavenge manifold bypass passage, such aspassage 98 and SMBV 97 shown in FIG. 1A). In this way, excess pressurein the scavenge exhaust manifold may be relieved by flowing at least aportion of the exhaust gases exhausted from the scavenge exhaust valvesto the scavenge exhaust manifold and then to the exhaust passage via thescavenge manifold bypass passage.

At 508, the method includes determining if it is possible to adjust theactuation state of the scavenge exhaust valves. As one example, VCTsystems may include hydraulically controlled valves that rely on oilpressure to operate and switch an activation state and/or timing profileof the valves. As such, in some examples, only when oil pressure hasreached a threshold pressure for switching a timing profile oractivation state of the scavenge exhaust valves may the activation stateof the scavenge exhaust valves be switched. In alternate embodiments,the scavenge exhaust valves may be adjusted in response to a differentvariable. If, at 508, it is determined that the activation state ortiming profile of the scavenge exhaust valves cannot be adjusted, themethod continues to 510 to maintain the scavenge exhaust valvesactivated and continue to modulate the BTCC valve. However, when theactivation state of the scavenge exhaust valves is able to be switched,the method continues to 512 to determine whether the scavenge exhaustvalves are able to switch between timing profiles. In one example, thescavenge exhaust valves may be switched between cam timing profiles(e.g., to adjust the opening and closing timing within the engine cycle)instead of being deactivated. If the scavenge exhaust valves cannot beswitched between timing profiles, the method continues to 514 todeactivate the scavenge exhaust valves (e.g., deactivate theactuation/timing mechanisms of the scavenge exhaust valves such that thescavenge exhaust valves remain closed and do not open at theirdesignated timing) and close (e.g., fully close) the BTCC valve. In someexamples, the method at 514 may include holding some crank hydrocarbonemissions within the scavenge exhaust manifold until the BTCC valve maybe opened again. Adjusting the scavenge exhaust valves and BTCC valve inthis way, while the engine is warming up, may increase low loadstability of the engine while reducing emissions during the cold start.

Alternatively at 512, if the scavenge exhaust valves may be switchedbetween timing profiles, the method instead proceeds to 516. At 516, themethod includes switching the timing of the scavenge exhaust valves toan early open/high lift profile (as shown at plot 326 of FIG. 3B, asdescribed above) and closing the BTCC valve. In one example, the methodat 516 may include advancing the timing (e.g., the opening timing) ofthe scavenge exhaust valves and/or increasing an amount of lift of thescavenge exhaust valves via switching the cam timing profile. In someexamples, the method at 516 may further include opening the scavengemanifold bypass valve to allow exhaust gases to flow from the scavengemanifold to the exhaust passage while the BTCC valve is closed. In thisembodiment of the method, the light-off catalyst may be disposeddownstream of where the scavenge manifold bypass passage couples to theexhaust passage (such as emission control device 72 shown in FIG. 1A).Thus, in this embodiment, there may be no additional light-off catalyst(such as a three-way catalyst) upstream of where the scavenge manifoldbypass passage couples to the exhaust passage.

Both of the methods at 516 and 514 continue to 530 to determine if acatalyst disposed in the exhaust passage is at (e.g., has reached) alight-off temperature. In one example, the catalyst may be part of oneor more emission control devices positioned in the exhaust (e.g., suchas emission control devices 70 and 72 shown in FIG. 1A). If the one ormore catalysts are at or above their light-off temperatures (e.g., forefficient catalyst operation), the method continues to 532 to adjustingthe timing of the scavenge exhaust valves based on engine conditions. Inone example, the method at 532 may include adjusting the scavengeexhaust valves to their default, or baseline timing (e.g., such as thetiming shown in FIG. 3A). The method then ends.

Alternately, if a temperature of the one or more catalysts is below thelight-off temperature, the method continues to 534 to further adjustengine operation to increase the temperature of the catalyst. In oneexample, as shown at 536, the method at 534 may include deactivating theblowdown exhaust valves of the outside cylinders (e.g., blowdown exhaustvalves 8 of cylinders 12 and 18 shown in FIG. 1A) while maintaining allthe scavenge exhaust valves (for all the outside cylinders and insidecylinders) active. For example, the inside cylinders may be positionedphysically between the outside cylinders. In this way, only exhaust gasfrom the inside cylinders may flow to the catalysts within the exhaustpassage. The method at 536 may further include maintaining fueling tothe cylinders with the deactivated blowdown exhaust valves but notsparking these cylinders (however spark is still delivered to thecylinders with the non-deactivated blowdown exhaust valves). In anotherexample, as shown at 538, the method at 534 may include decreasing anopening of the throttle (e.g., throttle 62 shown in FIG. 1A) and openinga valve in a second EGR passage disposed between the scavenge exhaustmanifold and the intake passage, downstream of the compressor andupstream of the throttle (e.g., second EGR passage 58 shown in FIG. 1A).This may cause intake air to flow in reverse through the second EGRpassage, from the intake passage to the scavenge exhaust manifold, andinto the cylinders via the scavenge exhaust valves. This may result inincreasing the temperature of blowthrough gases that are directed to theexhaust via the blowdown exhaust manifold, thereby increasing thetemperature of the catalyst. The method at 538 may be referred to hereinas an idle mode and may be explained in more detail below with referenceto FIG. 7A-7B. At 534, one of the methods at 536 and 538 may be chosenbased on the architecture of the engine system. For example, the methodat 538 may be used if the system includes the second EGR passage.Otherwise, the method at 536 may be used. In alternate embodiments, themethod at 534 may choose between the methods at 536 and 538 based onalternate engine operating conditions.

Returning to 502, if the scavenge exhaust valves are not defaultactivated, then they may be default deactivated (and thus closed). Inthis case, the method continues to 518 to advance a timing of the intakevalves (e.g., intake valves 2 and 4 shown in FIG. 1A) and retard atiming of the exhaust valves. Advancing the timing of the intake valvesmay be adjusting one or more valve timing mechanisms of the intakevalves to advance a closing timing of the intake valves. Further,retarding the timing of the exhaust valves may include retarding anopening timing of both the scavenge exhaust valves and the blowdownexhaust valves together (e.g., when they are controlled via the camtiming system) or retarding the opening timing of only the blowdownexhaust valves. These adjustments may increase combustion stabilityduring the cold start. At 520, the method includes determining if it ispossible to adjust the activation state or timing profile of thescavenge exhaust valves (e.g., similar to the method at 508, asdescribed above). If the scavenge exhaust valves cannot be adjusted(e.g., due to an oil pressure being below a threshold for switching thevalve activation state), the method continues to 522 to maintain thescavenge exhaust valves deactivated. Otherwise, if the scavenge exhaustvalves are able to be adjusted (or reactivated), the method continues to524 to determine whether it is possible to switch the scavenge exhaustvalves between timing profiles (e.g., similar to the method at 512, asdescribed above) If the scavenge exhaust valves cannot be switchedbetween profiles, the method continues to 526 to activate the scavengeexhaust valves and modulate the BTCC valve to control the EGR flowthrough the EGR passage and to the compressor inlet to a desired amount.However, if the scavenge exhaust valves are able to be switched betweenprofiles, the method instead continues to 528 to switch the profile ofthe scavenge exhaust valves to an early open/high lift and close theBTCC valve, as described above at 516. Both of the method at 526 and 528then continue to 530, as described above.

FIG. 16 shows a graph 1600 of operating the split exhaust engine systemin the cold start mode. Specifically, graph 1600 depicts an activationstate of the scavenge exhaust valves (where on is activated and off isdeactivated) at plot 1602, a position of the BTCC valve at plot 1604,EGR flow (e.g., an amount or flow rate of EGR flow through the EGRpassage 50 and to the compressor inlet, as shown in FIG. 1A) at plot1606, a temperature of an exhaust catalyst relative to a light-offtemperature of the catalyst at plot 1608, a position of an intakethrottle (e.g., throttle 62 shown in FIG. 1A) at plot 1610, a positionof a second, mid-pressure EGR valve disposed in a second (e.g.,mid-pressure) EGR passage (e.g., valve 59 in second EGR passage 58 shownin FIG. 1A) at plot 1612, and a cam timing of the intake valves at plot1614 and the exhaust valves (which may include the blowdown exhaustvalves and the scavenge exhaust valves when they are controlled on thesame cam timing system) at plot 1616 relative to their base timings B1(an example of the base cam timings of the intake and exhaust valves maybe shown in FIG. 3B, as described above). All plots are shown over timealong the x-axis.

Prior to time t1, the engine starts with the scavenge exhaust valvesdefault activated. As such, the scavenge exhaust valves may open andclose at their set timing in the engine cycle. At time t1, the BTCCvalve is opened for the initial crank. As such, the EGR flow begins toincrease after time t1 (and may increase and decrease over time with theopening and closing of the BTCC valve, respectively). After firing thefirst cylinder, the BTCC valve is modulated to control EGR flow to adesired level. Also between time t1 and time t2, the mid-pressure EGRvalve is closed and both the intake and exhaust valve timings are attheir base timings. At time t2, the scavenge exhaust valves can beadjusted (e.g., due to the oil pressure having reached a threshold toadjust the valves), so the scavenge exhaust valves are deactivated(e.g., turned off). After time t2, the catalyst temperature is stillbelow its light-off temperature T1. Thus, the throttle opening isdecreased and the mid-pressure EGR valve is opened to reverse flowthrough the system and send warmer blowthrough air to the catalystwithin the exhaust passage. This may result in warming of the catalystto a temperature above the light-off temperature T1.

During a different cold start in the split exhaust engine system, theengine may start with the scavenge exhaust valves default deactivated(e.g., off), as shown at time t3. At time t4, the intake cam timing ofthe intake valves is advanced and the exhaust cam timing of the blowdownexhaust valves is retarded (as shown at plot 328 in FIG. 3B, asdescribed above). At time t5, in response to the scavenge exhaust valvesbeing able to be adjusted, the scavenge exhaust valves are activated andthe BTCC valve is modulated to adjust EGR flow.

In this way, adjusting an activation state of the scavenge exhaustvalves while also controlling a position of the BTCC valve based ondesired EGR flow and a pressure in the scavenge exhaust manifold,exhaust emissions during the engine cold start may be reduced. Asdescribed above with reference to FIGS. 5 and 16, a method may include,during a cold start, adjusting a position of a first valve (BTCC valve)disposed in an exhaust gas recirculation (EGR) passage based on anengine operating condition, the EGR passage coupled between a firstexhaust manifold (scavenge manifold) coupled to a first set of exhaustvalves (scavenge exhaust valves) and an intake passage, upstream of acompressor, while flowing a portion of exhaust gases to an exhaustpassage including a turbine via a second set of exhaust valves (blowdownexhaust valves). A technical effect of adjusting the first valve and/orthe first set of exhaust valves in response to an engine operatingcondition during a cold start is reducing cold start emissions whilealso aiding in engine warmup, such as increasing a temperature of theengine cylinders and/or pistons and/or one or more exhaust catalysts. Inanother embodiment, a method may include, in response to select engineoperating conditions (such as a cold start and/or catalyst temperaturebelow a light-off temperature), deactivating one or more valves of a setof first exhaust valves (blowdown exhaust valves) coupled to a firstexhaust manifold coupled to an exhaust passage, while maintaining activeall valves of a set of second exhaust valves (scavenge exhaust valves)coupled to a second exhaust manifold coupled to an intake passage via anexhaust gas recirculation (EGR) passage. A technical effect ofdeactivating one or more of the blowdown exhaust valves (such as theblowdown exhaust valves of the outside cylinders, as described above at536 of method 500) during a cold start is increasing a temperature ofthe engine during the cold start and thus reducing engine emissionsduring the cold start (e.g., the catalyst may reach its light-offtemperature more quickly than if all the blowdown exhaust valves stayedactivated). In yet another embodiment, a method may include, while botha first exhaust valve (scavenge exhaust valve) and second exhaust valve(blowdown exhaust valve) of a cylinder are open, routing intake airthrough a flow passage (e.g., mid-pressure EGR passage) coupled betweenan intake passage and a first exhaust manifold coupled to the firstexhaust valve; and further routing the intake air through the firstexhaust valve, into the cylinder, and out of the second exhaust valve toa second exhaust manifold (blowdown exhaust manifold) coupled to anexhaust passage including a turbine. A technical effect of routing theintake air in this way while both the first and second exhaust valvesare open, responsive to a temperature of a catalyst disposed in theexhaust passage, downstream of the turbine, being below a thresholdtemperature, is increasing the temperature of the blowthrough air to theexhaust passage and thus increasing the temperature of the catalyst. Asa result, the catalyst may reach its light-off temperature more quicklyand engine emissions during the cold start may be reduced.

Turning now to FIG. 6, a method 600 for operating the engine system in aDFSO mode is shown. Method 600 may continue from 410 of method 400, asdescribed above. At 602, the method includes stopping fueling to allcylinders to initiate the DFSO mode. The method continues to 604 todeactivate the blowdown exhaust valve (e.g., blowdown exhaust valves 8shown in FIG. 1A) of one or more cylinders and maintain all the scavengeexhaust valves active. In one example, the method at 604 includesdeactivating the blowdown exhaust valve of each and every cylinder sothat no exhaust gas is directed to the catalyst(s) disposed within theexhaust passage. As a result, oxygen to the catalyst (e.g., three-waycatalyst) may be reduced, thereby preserving catalyst function. Inanother example, the method at 604 includes deactivating the blowdownexhaust valve of a select number of cylinders (e.g., only a portion ofall the engine cylinders). The select number may be based on pedalposition (e.g., driver torque demand), estimated exhaust temperature,turbine speed of a turbine disposed in the exhaust passage, and/ordeceleration rate of the vehicle (e.g., rate of decrease in vehiclespeed). As one example, the method at 604 may include deactivating allBDVs (e.g., each BDV of each cylinder). However, in this example, theturbine may stop rotating and the catalyst may cool off. Thus, themethods at 602 and 604 may alternatively include maintaining active theBDVs of one or more cylinders and firing the corresponding one or morecylinders to reduce engine braking, spin up the turbine, and maintaincatalyst temperature (e.g., without the catalyst temperaturedecreasing). The amount of spark on the firing cylinder(s) may beretarded to reduce torque and increase exhaust heat and engineefficiency. Then, the firing fraction (e.g., amount of cylinders firedwith active BDVs) and spark for the firing cylinder(s) may be determinedbased on the pedal position, estimated exhaust temperature, and vehicledeceleration rate. As another example, if the turbine speed is below athreshold speed, the select number of BDVs to deactivate may be smallerthan if the turbine speed were above the threshold speed. In this way,turbo lag following the DFSO event may be reduced. As an example, thecontroller may make a logical determination of the number of blowdownexhaust valves to deactivate at 604 and/or the number of cylinders tostop fueling as a function of turbine speed, pedal position, estimatedexhaust temperature, and/or vehicle deceleration rate. The controllermay then send a control signal to an actuator of the blowdown exhaustvalves to deactivate the determined number of blowdown exhaust valves.As one example, each blowdown exhaust valve may include an actuator(such as actuator 103 shown in FIG. 1A) that may be used to deactivateand reactivate the associated blowdown exhaust valve.

At 606, the method includes determining if it is time to reactivate theblowdown exhaust valves of the deactivated cylinders. As one example, itmay be determined that it is time to reactivate the deactivated blowdownexhaust valves at the end of the DFSO event, which may be indicated byan increase in vehicle speed and/or an depression of an acceleratorpedal (e.g., a pedal position depressed beyond a threshold position). Ifit is not time to reactivate the blowdown exhaust valves, the methodproceeds to 608 to continue operating the engine with the deactivatedcylinders (e.g., cylinders with the deactivated blowdown exhaustvalves). Otherwise, if the DFSO had ended and/or it is time toreactivate the cylinders, the method continues to 610 to reactivate theblowdown exhaust valves of the deactivated cylinders. As an example,reactivating the blowdown exhaust valves of the deactivated cylindersmay include sending a signal to one or more valve actuation mechanismsof the blowdown exhaust valves to resume operating the blowdown exhaustvalves at their set timing. Further, reactivating the blowdown exhaustvalves may include sparking each deactivated cylinder following anintake valve closing event and then opening the deactivated blowdownexhaust valve. At 612, the method includes reactivating fuel injectionto the cylinders and reducing the amount of fuel enrichment to thecylinders. In one example, this may include reducing the amount of fuelinjected into the cylinders compared to a standard fuel injection amountfollowing a DFSO event (e.g., without any blowdown exhaust valvedeactivation). Since less oxygen was exhausted to the catalyst duringDFSO due to the blowdown exhaust valve deactivation, less fuelenrichment may be needed following the DFSO event. As a result, fueleconomy is increased vs. traditional DFSO.

FIG. 17 shows a graph 1700 of operating the split exhaust engine systemin the DFSO mode. Specifically, graph 1700 depicts a pedal position(e.g., accelerator pedal position) at plot 1702, a fueling amount(injected into engine cylinders) at plot 1704, an activation state of ablowdown exhaust valve (BDV) of a first cylinder at plot 1706, anactivation state of a blowdown exhaust valve (BDV) of a second cylinderat plot 1708, an activation state of a blowdown exhaust valve (BDV) of athird cylinder at plot 1710, an activation state of a blowdown exhaustvalve (BDV) of a fourth cylinder at plot 1712, turbine speed at plot1714, and an activation state of the scavenge exhaust valves of allcylinders (SVs) at plot 1716.

Prior to time t1, the pedal position is relatively steady and the BDVsand SVs of all four cylinders are activated (e.g., on). As such, eachBDV may open and close according to a set timing in the engine cycle. Attime t1, the pedal position decreases, indicating a deceleration event.A DFSO event is initiated by cutting off fueling to a portion of theengine cylinders. As shown at time t1, fueling may be stopped tocylinders 2-4, but maintained at cylinder 1 in order to maintain enginespeed at a threshold speed, keep the turbine spinning, and maintain thecatalyst warm and at stoichiometry (and thus fueling does not go to zerobetween time t1 and time t2). In response to the DFSO event anddeactivating fueling to cylinders 2-4, the BDVs of cylinders 2, 3, and 4are deactivated while the SVs remain activated for all cylinders. As aresult, no exhaust gas travels to the exhaust passage from cylinders 2,3, and 4. Instead, exhaust gases from the deactivated cylinders aredirected to the intake passage via the SVs and scavenge exhaustmanifold. At time t2, the pedal position increases and the DFSO eventends. The BDVs of cylinders 2, 3, and 4 are reactivated and the fuelingamount to the cylinders may be reduced slightly compared to a DFSO eventwhere no BDVs are deactivated.

At time t3, another DFSO event occurs. In response to the DFSO event andthe turbine speed being at a higher level (e.g., higher than at time t1during the first DFSO event), the BDVs of cylinders 1, 2, 3, and 4 aredeactivated. Thus, all BDVs of all cylinders are deactivated (e.g., agreater number of BDVs are deactivated at time t3 than at time t1 due tothe higher turbine speed at time t3). In response to the DFSO eventending at time t3, all the BDVs are reactivated.

In this way, in response to select engine operating conditions (such asa DFSO condition where fueling to engine cylinders is disabled), one ormore valves of a set of first exhaust valves (BDVs) coupled to a firstexhaust manifold coupled to an exhaust passage may be deactivated, whilemaintaining active all valves of a set of second exhaust valves (SVs)coupled to a second exhaust manifold coupled to an intake passage via anexhaust gas recirculation (EGR) passage. A technical effect ofdeactivating one or more BDVs during the DFSO event is reducing theamount of oxygen directed to a catalyst in the exhaust passage duringDFSO. As a result, catalyst performance may be improved and engineemissions may be reduced. Further, reducing the amount of oxygendirected to the catalyst during DFSO may allow for less fuel enrichmentto be used upon reactivation of the BDVs, at the conclusion of the DFSOevent, thereby increasing fuel economy of the engine system.

Turning now to FIGS. 7A-7B, a method 700 for operating the engine systemin a part throttle mode is shown. Method 700 may continue from 414 ofmethod 400, as described above. At 702, the method includes determiningwhether conditions are met for operating in a hot pipe mode. In oneexample, the split exhaust engine system may include a passage coupledbetween the scavenge exhaust manifold and the intake passage, downstreamof an intake throttle (e.g., passage 30 shown in FIG. 1A, referred toherein as a hot pipe). However, in some embodiments, the split exhaustengine system may not include the hot pipe and thus hot pipe modeconditions would not be met. In one example, the hot pipe mode may bethe default mode for best fuel economy when the engine is throttled(e.g., when the amount of throttle opening is less than wide openthrottle). Conditions for entering the hot pipe mode include the enginesystem including the hot pipe and may additionally include the enginenot being knock limited. For example, when engine load is below a lowerthreshold load (e.g., at very light loads) and no more EGR may betolerated by the engine, the hot pipe valve may be closed and the hotpipe conditions may not be met. In another example, when engine load isabove an upper threshold load (e.g., at high engine loads), knock mayalso occur and thus the hot pipe valve may be closed to push more EGR tothe compressor inlet for engine cooling. Thus, the conditions forentering the hot pipe mode may include the engine not being knocklimited (e.g., the chance of engine knocking being below a threshold)and being able to tolerate increased EGR.

If conditions are met for entering the hot pipe mode, the methodcontinues to 704. At 704, the method includes closing (e.g., fullyclosing) the intake throttle, opening the BTCC valve (e.g., valve 54shown in FIG. 1A), and opening the hot pipe valve (e.g., valve 32 shownin FIG. 1A). As a result, intake air from the intake passage, upstreamof the compressor, may be directed into the EGR passage (e.g., first EGRpassage 50 shown in FIG. 1A, through an EGR cooler (e.g., EGR cooler 52shown in FIG. 1A), into the scavenge exhaust manifold, through the hotpipe (e.g., hot pipe 30 shown in FIG. 1A), into the intake manifold,downstream of the intake throttle, and into the engine cylinders. Bypassing through the EGR cooler, the intake air is heated before enteringthe engine cylinders. This may increase MAP, reduce intake pumping workof the engine, increase fuel economy, and decrease engine emissions.Further, this operation may also reduce scavenge manifold pressure,thereby increasing EGR flow. This intake air may then be combustedwithin the engine cylinders. A first portion of the combustion gases arethen exhausted from the engine cylinders into the blowdown exhaustmanifold via the blowdown exhaust valves. The first portion ofcombustion gases then travels through the exhaust passage to the turbineand one or more emission control devices. A second portion of thecombustion gases are exhausted from the engine cylinders to the scavengeexhaust manifold via the scavenge exhaust valves. The second portion ofexhaust gases are mixed with intake air within the scavenge exhaustmanifold and then the mixture is routed to the intake manifold via thehot pipe. This mixing may reduce the impact of any one cylinder on EGRmixing and thus reduce pushback and manifold tuning.

At 706, the method includes adjusting (e.g., adjusting a position of)the hot pipe valve based on a desired MAP and adjusting exhaust camtiming based on engine load. As one example, the method adjusts theamount of opening (or position) of the hot pipe valve based on a desiredMAP which may be determined based on engine operating conditions. Forexample, the controller may determine a control signal to send to thehot pipe valve actuator based on a determination of the desired MAP. Thecontroller may determine the control signal through a determination thatdirectly takes into account a determined desired MAP, such as increasingthe amount of opening of the hot pipe valve with increasing desired MAP.The controller may alternatively determine the amount of opening of thehot pipe valve based on a calculation using a look-up table with theinput being desired MAP and the output being the signal of the hot pipevalve position. As another example, the controller may make a logicaldetermination (e.g., regarding an actuator of the cam timing system ofthe scavenge and blowdown exhaust valves) based on logic rules that area function of engine load. The controller may then generate a controlsignal that is sent to an exhaust valve cam timing actuator. Forexample, as engine load increases, the cam timing of the exhaust valves(e.g., blowdown and scavenge exhaust valves if they are controlled viathe same cam system) may be advanced.

At 708, the method includes determining whether conditions are met for aVDE mode where one or more blowdown exhaust valves are deactivated. Inone example, conditions for entering the VDE mode may include one ormore of a turbine speed above a threshold speed (e.g., that may be basedon a speed at which turbo lag may occur upon an increase in torquedemand) and/or engine load below a threshold load. If conditions foroperating in the VDE mode are met, the method continues to 710. At 710,the method includes deactivating the blowdown exhaust valve of one ormore cylinders. In one example, the number of cylinders for which theblowdown exhaust valve is deactivated may be based on engine load ortorque demand. Specifically, as engine load decreases, the number ofcylinders with deactivated blowdown exhaust valves may increase. Forexample, during a first condition, at part throttle when engine torquedemand is below a lower threshold level, the blowdown exhaust valves ofeach and every engine cylinder may be deactivated. During a secondcondition, at the part throttle condition when engine torque demand isabove the lower threshold level, only a portion of the blowdown exhaustvalves of the engine cylinders may be deactivated, where the portion(and thus number of cylinder with deactivated blowdown exhaust valves)decreases as torque demand increases further above the lower thresholdlevel. Additionally at 710, all scavenge exhaust valves of all thecylinders are maintained activated during the blowdown exhaust valvedeactivation. Further, the method at 710 may include disabling spark to,but still fueling, the cylinders with deactivated blowdown exhaustvalves. In this way, a firing decision can be made later in the enginecycle (since fuel is still injected). Further, fueling the deactivatedcylinders and pumping the mixture to firing cylinders (e.g., cylinderswithout deactivated blowdown exhaust valves) may increase fuelevaporation on the firing cylinders (and thus reduce smoke). Further,the method at 710 may include maintaining the hot pipe valve open andthe throttle closed during the blowdown valve deactivation. In someexamples, the method at 710 may include reactivating the deactivatedblowdown exhaust valves in response to an increase in torque demand overa threshold and/or the throttle being commanded to fully open (or thethrottle opening). The method may then end.

Returning to 702, if the conditions for the hot pipe mode are not met,the method continues to 712 to determine whether the conditions are metfor an EIVC (early intake valve closing) mode. In one example, thedecision to enter the EIVC mode may be a function of MAP, engine speed,and engine temperature when engine load is below a threshold load. Inone example, conditions for entering the EIVC mode may include engineload being below the threshold load and MAP being at atmosphericpressure (e.g., when the engine is not boosted). If conditions are metfor the EIVC mode, the method continues to 714. At 714, the methodincludes deactivating the intake valves and opening the scavenge exhaustvalves (at the set timing for each cylinder) to induct air into theengine cylinders via the scavenge exhaust valves, instead of via theintake valves. Specifically, the method at 714 may include deactivatingthe intake valves (e.g., both intake valves) of all engine cylinders sothat no intake air is inducted into the cylinders via the intake valves.The method at 714 may further include opening (e.g., fully opening) theBTCC valve (if not already open).

At 716, the method includes retarding the blowdown exhaust valve andscavenge exhaust valve timing to reverse the direction of the intake airinto the cylinder (e.g., to enter the cylinder via the scavenge exhaustvalves). In one example, the method at 716 may include operating boththe scavenge exhaust valves and blowdown exhaust valves at a maximumamount of exhaust cam retard (e.g., when controlled by the same camsystem). As another example, with a cam in cam type control system, themethod at 716 may include setting the closing of the blowdown exhaustvalves to TDC and advancing the scavenge exhaust valves to decreaseoverlap between the scavenge and blowdown exhaust valve of eachcylinder. As yet another example, with a cam profile switching system,the method at 716 may include changing the cam profiles (e.g., of thescavenge exhaust valves and blowdown exhaust valves) to a best timingfor EIVC. As a result of this operation, in the EIVC mode, intake air isinducted to the engine cylinders from the intake passage via the EGRpassage, scavenge exhaust manifold, and scavenge exhaust valves.Following combustion within the engine cylinders, exhaust gases areexhausted to the exhaust passage via the blowdown exhaust valves. Inthis way, pumping work of the cylinders during low load is reduced.Additionally, charge motion is improved for increased combustionstability.

Returning to 712, if conditions are not met for the EIVC mode, themethod continues to 718 to determine whether conditions are met forclosing a charge motion control valve (CMCV) coupled to an intake portof one intake runner of each cylinder (e.g., such as CMCVs 24 shown inFIG. 1A). In one example, the conditions for closing the CMCVs mayinclude engine load being below a lower threshold load. If theconditions for closing the CMCVs are met, the method continues to 720 toclose the CMCV coupled to the intake port of the intake valve of eachcylinder (e.g., CMCVs 24 shown in FIG. 1A). For example, the method at720 may include adjusting the CMCVs to at least partially block intakeflow to the intake valves (e.g., one intake valve, as shown in FIG. 1A)of each cylinder. As a result, the turbulence (or swirl) of the intakeair flow entering the engine cylinders may increase, thereby allowingthe intake air to scavenge an increased amount of exhaust gas frominside the engine cylinders and to the scavenge exhaust manifold.

Otherwise, if conditions for closing the CMCV are not met (or they arealready closed), the method continues to 722 to determine whetherconditions are met for an idle boost mode. In one example, the conditionfor entering the idle mode includes when the engine is idling (e.g.,when vehicle speed is below a threshold vehicle speed, which may bezero, and/or when engine speed is below a threshold engine speed). Asone example, operating in the idle boost mode may allow for the scavengemanifold to be pressurized, thereby resulting in air purging some of theexhaust gases trapped in the cylinders. This may increase combustionstability and/or increasing warming of one or more catalysts disposed inthe exhaust passage. Thus, in one example, a condition for entering theidle boost mode includes when there is a desired for purging gases fromthe engine cylinders. If the conditions are met at 722, the methodcontinues to 724.

The method at 724 includes closing the turbocharger wastegate (e.g.,wastegate valve 76 shown in FIG. 1A) to increase boost pressure andopening a valve in an idle boost pipe (e.g., valve 59 in second EGRpassage 58 shown in FIG. 1A). The idle boost pipe may also be referredto as a second, or mid-pressure, EGR passage and may be coupled betweenthe scavenge exhaust manifold and the intake passage, downstream of thecompressor. By opening the valve in the idle boost pipe while engineload is below a threshold, intake air flow from downstream of thecompressor may flow through the idle boost pipe and into the scavengeexhaust manifold. Then, while both the scavenge exhaust valve andblowdown exhaust valve of a same cylinder are open, the intake air fromthe idle boost pipe may flow into the engine cylinder via the scavengeexhaust valve and then to the exhaust passage via the blowdown exhaustvalve. This may be referred to as blowthrough to the exhaust. Thisallows for purging of residual exhaust gases from within the enginecylinders to the exhaust passage at idle conditions, thereby increasingengine stability. The method at 724 may further include modulating theposition of the BTCC valve to achieve a desired blowthrough amountduring an overlap (e.g., opening overlap) period between the blowdownexhaust valve and scavenge exhaust valve of each cylinder. As oneexample, the desired blowthrough amount during the overlap period may bedetermined based on engine stability. For example, purging the exhaustgas from the cylinders may improve the burn rate and allow the cylinderto be fueled rich, which may increase stability. However, too muchblowthrough may decrease fuel economy and reduce catalyst temperatures.For example, modulating the position of the BTCC valve includes openingand closing the BTCC valve to control a pressure of the scavenge exhaustmanifold to level that produces a desired amount of blowthrough from thescavenge exhaust valve to the blowdown exhaust valve while the scavengeand blowdown exhaust valves are both open. As one example, decreasingthe amount of opening of the BTCC valve and/or closing the BTCC valvefor a longer duration may increase the pressure within the scavengeexhaust manifold (e.g., above the pressure in the exhaust passage) andincrease the amount of blowthrough to the exhaust. As yet anotherexample, the controller may open the scavenge manifold bypass valve(e.g., SMBV 97 shown in FIG. 1A) and adjust a position of the BTCC valveto increase the scavenge exhaust manifold pressure above the exhaustpressure. The excess air in the exhaust, created by the blowthrough, mayallow for rich in-cylinder conditions that increase engine stabilitywhile still maintaining an overall stoichiometric air-fuel ratiodownstream of a catalyst for reduced emissions. In some examples, themethod at 724 may additionally include decreasing an amount of openingof (or fully closing) the intake throttle.

Continuing to 726, the method includes controlling an exhaust and intakevalve overlap to regulate flow to the intake manifold from the scavengeexhaust manifold. For example, the method at 726 may include adjusting atiming of the scavenge exhaust valve and the intake valve of a cylinderto adjust an amount of valve overlap between the intake valve andscavenge exhaust valve and control a flow of air from the scavengeexhaust manifold to the intake manifold to a desired level. The desiredlevel of air to the intake manifold may vary based on engine load. Forexample, in response to engine load increasing, the controller may sendsignals to timing actuators of the scavenge exhaust valves and intakevalves to increase the amount of valve overlap between the intake valveand scavenge valve of each cylinder, thereby increasing the air flowfrom the scavenge manifold to the intake manifold. As one example, thecontroller may make a logical determination regarding the timing of thescavenge exhaust valve and intake valve based on logic rules that are afunction of engine load. The controller may then generate a controlsignal that is sent to the intake and exhaust valve timing actuators.

The method may then proceed to 728 to further control boost andblowthrough to desired levels by one or more of activating (andoperating) an electric compressor (e.g., electric compressor 60 shown inFIG. 1A), increasing the opening of the turbocharger wastegate,adjusting spark retard, and/or adjusting cam timing to adjust thescavenge valve and blowdown valve overlap. As one example, the method at728 may include increasing an amount of opening of the wastegate inresponse to a request to decrease a pressure of the scavenge exhaustmanifold and reduce an amount of blowthrough air flowing from thescavenge exhaust manifold to the blowdown exhaust manifold. As anotherexample, operating the electric compressor may enhance the blowthroughcapability by providing increased pressure to the scavenge exhaustmanifold. In yet another example, increased spark retard may be used inresponse to a request for more blowthrough to the exhaust. In yetanother example, in systems where the blowdown and scavenge exhaustvalve overlap can be varied (e.g., via a cam in cam type system), theoverlap may be increased to increase blowthrough.

Returning to 722, if the conditions are not met for the idle boost mode,the method continues to 730 of FIG. 7B. As one example, conditions maynot be met for the idle boost mode if it is determined that it is timeto measure EGR pullback into a scavenge exhaust valve runner. At 730,the method includes determining whether the engine is idling (e.g., ifan accelerator pedal is not depressed and/or the engine is decoupledfrom the drive train of the vehicle). If the engine is idling, themethod continues to 732 to determine the amount of EGR pulled back intothe runner (e.g., exhaust port) of each scavenge exhaust valve based onan oxygen level measured via an oxygen sensor positioned in the exhaustrunner of each scavenge exhaust valve. For example, there may be anoxygen sensor positioned in the exhaust runner of each scavenge exhaustvalve of each cylinder (e.g., such as the oxygen sensors 38 shown inFIG. 1A) and thus, an output of each oxygen sensor may give an estimateof the EGR pullback for each cylinder. At 734, the method includesadjusting the exhaust valve timing (e.g., of the scavenge exhaust valvesand blowdown exhaust valves) to adjust the EGR flow based on theestimated amount of EGR pullback at each engine cylinder. For example,this may include advancing the exhaust valve timing to increase EGR flowresponsive to the estimated EGR pullback increasing. As another example,the controller may make a logical determination (e.g., regarding theexhaust valve timing) based on logic rules that are a function of EGRpullback in the scavenge valve exhaust runners. The controller may thengenerate a control signal that is sent to the exhaust valve timingactuators. Alternatively at 730, if the engine is not idling, the methodends.

FIGS. 18A-18B show a graph 1800 of operating the split exhaust enginesystem in the part throttle mode. Specifically, graph 1800 depictsengine load at plot 1802, a position of an intake throttle (e.g., intakethrottle 62 shown in FIG. 1A) at plot 1804, a position of the BTCC valve(e.g., valve 54 shown in FIG. 1A) at plot 1806, a position of the hotpipe valve (e.g., valve 32 shown in FIG. 1A) at plot 1808, MAP relativeto atmospheric pressure (ATM) at plot 1810, an activation state (e.g.,on and operating or off and disabled) of the intake valves at plot 1812,an activation state of the scavenge exhaust valves (e.g., valves 6 shownin FIG. 1A) at plot 1814, a position of the CMCVs (e.g., CMCVs 24 shownin FIG. 1A) at plot 1816, a position of the idle boost pipe valve (e.g.,valve 59 shown in FIG. 1A) at plot 1818, a position of the turbochargerwastegate (e.g., wastegate 76 shown in FIG. 1A) at plot 1820, anoperation state of an electric compressor (e.g., electric compressor 60shown in FIG. 1A, where on indicates the electric compressor is beingdriven by an electric motor of the electric compressor), a pressure inthe scavenge exhaust manifold (e.g., output from pressure sensor 34shown in FIG. 1A) at plot 1824, a pressure at the compressor inlet ofthe turbocharger compressor (e.g., output from pressure sensor 31 shownin FIG. 1A) at plot 1826, an activation state of a first blowdownexhaust valve (BDV) of a first cylinder at plot 1828, and an activationstate of blowdown exhaust valves (BDVs) of a second, third, and fourthcylinder at plot 1830. Though the valve positions may be shown as openand closed in FIGS. 18A-18B, in alternate embodiments, the valves may beadjusted into a plurality of positions between fully open and fullyclosed.

Prior to time t1, engine load is above a lower threshold load L1 and thethrottle is fully open. An engine load below the lower threshold load L1may be indicative of a low load condition where the throttle is at leastpartially closed (e.g., not fully open). Thus, prior to time t1, engineload is above this low load threshold. At time t1, engine load decreasesbelow the lower threshold load and the throttle position decreases(e.g., the amount of opening of the throttle decreases). The engine mayalso be boosted at time t1 (e.g., MAP greater than ATM). In response tothis low load condition at time t1, just after time t1 the throttle isclosed, the BTCC valve is opened, and the hot pipe valve is opened tooperate the engine in a hot pipe mode. The CMCVs may be maintainedclosed during the low load condition at time t1. Further, the BDV of thefirst cylinder may be deactivated just after time t1, responsive to theengine load being below the lower threshold load. However, the BDVs ofthe second, third, and fourth cylinder may remain activated. As a resultno exhaust gas travels to the exhaust passage from the first cylinderwhile the BDV of the first cylinder is deactivated. In alternateembodiments, additional BDVs of additional cylinders may be deactivatedin response to the low load condition. For example, if the engine loadbetween time t1 and time t2 were further below the lower threshold loadL1, the controller may deactivate the BDVs of two or more cylinders(instead of just one, as shown at time t1).

At time t2, engine load increases above the lower threshold load L1 andthe throttle position gradually returns to the fully open position(e.g., wide open throttle). Thus, the hot pipe valve is closed at timet2. Further, the CMCVs are opened and all the BDVs are activated at timet2. Also at time t2, the electric compressor is turned on to increaseboost. In response to the compressor inlet pressure being greater thanthe scavenge exhaust manifold pressure at time t2, the BTCC valve isclosed. The BTCC valve is reopened prior to time t3. In response to theBTCC valve being opened, the CMCVs are closed.

At time t3, engine load again falls below the lower threshold load L1.In response to this low load condition and conditions for the EIVC modebeing met, the intake valves of all the engine cylinders are deactivatedat time t3. In some examples, the exhaust cam timing of the BDVs and SVsmay be retarded to allow intake air to be inducted into the enginecylinders via the SVs and exhausted out of the BDVs during the EIVCmode. At time t4, engine load increases above the lower threshold loadL1. As a result, the intake valves are reactivated. Prior to time t5,the wastegate opens. In one example, the wastegate may open responsiveto the turbine speed increasing above a threshold turbine speed. Forexample, a turbine speed over the threshold turbine speed may result ina compressor outlet temperature that is higher than an upper threshold(e.g., for reducing turbocharger degradation).

At time t5, engine load again falls below the lower threshold load L1.In response to this low load condition and conditions for the idle boostmode being met, the idle boost pipe valve is opened and the wastegate isclosed. Additionally, the BTCC valve is modulated to achieve a desiredblowthrough amount during the BDV and SV overlap period. At time t6,engine load increases above the lower threshold load and the idle boostpipe valve is closed. In this way, reverse flow through the EGR passageto the engine cylinders via the scavenge exhaust valves at a partthrottle condition, which may cause decreased mixing and cylinderbalance, may be reduced. As one embodiment of a method during the partthrottle condition, a method includes routing intake air from an intakepassage to a first exhaust manifold (scavenge manifold) coupled to afirst set of cylinder exhaust valves (scavenge exhaust valves) via anexhaust gas recirculation (EGR) passage; heating the intake air as itpasses through an EGR cooler in the EGR passage; routing the heatedintake air to an intake manifold, downstream of an intake throttle, viaa flow passage (hot pipe) coupled between the first exhaust manifold andthe intake manifold; and exhausting combustion gases via a second set ofcylinder exhaust valves (blowdown exhaust valves) to a second exhaustmanifold coupled to an exhaust passage. A technical effect of routingthe intake air in this way, through the hot pipe, during a part throttlecondition (or when engine load is below a threshold), is increasingmixing of EGR from each cylinder with incoming intake air, reducingpumping work of the cylinders, heating the intake air via the EGR coolerto increase MAP and further reduce intake pumping, and increasing fueleconomy and reducing emissions. As another embodiment of a method duringthe part throttle condition, a method includes, in response to engineload below a threshold, deactivating all intake valves of an enginecylinder while operating a first exhaust valve (scavenge exhaust valve)coupled to an exhaust gas recirculation (EGR) passage coupled to anintake passage and a second exhaust valve (blowdown exhaust valve)coupled to an exhaust passage at different timings; and routing intakeair from the intake passage, through the EGR passage, and into theengine cylinder via the first exhaust valve. A technical effect ofdeactivating all the intake valves during the part throttle condition iswarming the intake air via an EGR cooler disposed in the EGR passage,reducing pumping work, and increasing fuel economy. As yet anotherembodiment of a method during the part throttle condition, a methodincludes, in response to engine load below a lower threshold load,adjusting a first set of swirl valves (e.g., CMCVs) coupled upstream ofa first set of intake valves to at least partially block intake air flowto the first set of intake valves, where each cylinder includes twointake valves including one of the first set of intake valves and twoexhaust valves. A technical effect of adjusting the first set of swirlvalves to at least partially block the intake air flow to the first setof intake valves is increasing turbulence of intake air flow enteringthe cylinders via the first set of intake valves, thereby increasing thescavenging of the residual burned exhaust gases from the combustionchambers. As a result, engine emissions may be reduced and engineefficiency may be increased. As still another embodiment of a methodduring the part throttle condition, a method includes, in response toengine load below a threshold and while a first set of exhaust valvesand second set of exhaust valves are open at a same time: routing intakeair through a secondary flow passage (idle boost passage) coupledbetween an intake passage, downstream of a compressor, and a firstexhaust manifold, the first exhaust manifold coupled to the first set ofexhaust valves; heating the intake air routed through the secondary flowpassage via an EGR cooler coupled to the first exhaust manifold; androuting the heated intake air through engine cylinders and to a secondexhaust manifold, the second exhaust manifold coupled to the second setof exhaust valves and an exhaust passage including a turbine, via thefirst set of exhaust valves and the second set of exhaust valves. Thetechnical effect of routing the intake air through the secondary flowpassage in this way, during the engine load below the threshold, isenabling residual exhaust gas to be pushed out of the cylinder and intothe exhaust passage prior to the closing of the second exhaust valve. Asa result, engine efficiency and fuel economy may be increased, even atpart throttle conditions.

FIG. 8 shows a method 800 for operating the engine system in an electricboost mode. Method 800 may continue from 418 of method 400, as describedabove. Thus, during method 800, the electric motor of the electriccompressor may be driving the electric compressor (e.g., driving a rotorof the electric compressor to increase the pressure of the intake air).At 802, the method includes determining if a compressor inlet pressureis greater than a scavenge manifold pressure. As one example, thecompressor inlet pressure may be a pressure at the inlet (or directlyupstream of) the turbocharger compressor (e.g., compressor 162 shown inFIG. 1A). As another example, the compressor inlet pressure may be apressure at an outlet of the EGR passage (e.g., where passage 50 couplesto the intake passage in FIG. 1A, upstream of compressor 162). In oneexample, the compressor inlet pressure may be measured via a pressuresensor positioned in the intake passage upstream of the turbochargercompressor (e.g., pressure sensor 31 shown in FIG. 1A). In an alternateexample, the compressor inlet pressure may be estimated by thecontroller based one or more alternate engine operating parameters (suchas a pressure upstream of where the electric compressor couples to theintake passage). Additionally, the scavenge manifold pressure may be apressure of the scavenge exhaust manifold (e.g., scavenge exhaustmanifold 80 shown in FIG. 1A). In one example, the scavenge manifoldpressure may be measured by a pressure sensor disposed in the scavengemanifold (e.g., pressure sensor 34 shown in FIG. 1A). In anotherexample, the scavenge manifold pressure may be estimated or measured viaa plurality of pressure sensors positioned in exhaust runners of thescavenge exhaust valves.

If the compressor inlet pressure is greater than the scavenge manifoldpressure, the method continues to 804 to control (e.g., adjust) aposition of the BTCC valve (e.g., valve 54 shown in FIG. 1A) and/ordeactivate the scavenge exhaust valves (SVs, e.g., exhaust valves 6shown in FIG. 1A) to reduce blowthrough to the exhaust. In one example,the method at 804 may include one or more of decreasing the amount ofopening of the BTCC valve and deactivating the SVs in response to apressure of the scavenge manifold being less than an inlet pressure ofthe turbocharger compressor while the electric motor is driving theelectric compressor. In one example, the BTCC valve may be atwo-position valve adjustable into a fully open and fully closedposition. In another example, the BTCC valve may be a continuouslyadjustable valve adjustable into the fully open position, fully closedposition, and a plurality of positions between fully open and fullyclosed. In this example, an amount of decreasing the amount of openingof the BTCC valve may increase as the amount the scavenge manifoldpressure is below the compressor inlet pressure decreases. In anotherexample, the controller may deactivate the SVs if the scavenge manifoldpressure is a threshold amount below the compressor inlet pressure. Asone example, the method adjusts the amount of reducing the opening ofthe BTCC valve based on the scavenge manifold pressure. For example, thecontroller may determine a control signal to send to the BTCC valveactuator (or the SV actuator which controls an activation state of theSVs) based on a determination of the scavenge manifold pressure. Thecontroller may determine the position of the BTCC valve (open, closed,or a position between fully open and fully closed) through adetermination that directly takes into account a determined scavengemanifold pressure, such as decreasing the amount of opening as thescavenge manifold pressure decreases. The controller may alternativelydetermine the position of the BTCC valve, or an activation state of theSVs, based on a calculation using a look-up table with the input beingscavenge manifold pressure and the output being BTCC valve position (orSV activation state). As another example, the controller may make alogical determination (e.g., regarding a position of the BTCC valve)based on logic rules that are a function of scavenge manifold pressure.The controller may then generate a control signal that is sent to theactuator of the BTCC valve (and/or the SVs). Adjusting the BTCC valveand/or SVs in this way at 804 may reduce the reverse flow of gases fromthe scavenge manifold to the exhaust manifold and exhaust passage viathe SVs and BDVs that may occur due to the scavenge manifold being at alower pressure than the intake passage, at the compressor inlet.

The method continues to 808 to determine whether the electric motor hasstopped driving the electric compressor (e.g., the electric compressoris no longer operating and boosting the intake air). If the electricmotor has stopped driving the electric compressor, the method continuesto 812 to reactivate the SVs (if they were deactivated at 804) and/oropen the BTCC valve (if it was closed or the amount of opening wasreduced at 804). The method at 812 further includes adjusting theposition of the BTCC valve based on a desired EGR flow amount. As oneexample, the controller may make a logical determination (e.g.,regarding a position of the BTCC valve) based on logic rules that are afunction of a determined desired EGR flow amount. The controller maythen generate a control signal that is sent to the actuator of the BTCCvalve. Additionally or alternatively at 812, the method may includereturning to 420 of method 400.

Returning to 808, if the electric motor is still driving the electriccompressor, the method continues to 810 to continue adjusting the BTCCvalve and SVs based on the scavenge manifold pressure, as describedabove and below. The method may then return to 802 to recheck thescavenge manifold pressure relative to the compressor inlet pressure. Ifthe compressor inlet pressure is no longer greater than the scavengemanifold pressure, the method may continue to 806 to reopen the BTCCvalve if it was closed and/or reactivate the SVs if they weredeactivated. The BTCC valve is then controlled (e.g., adjusted) todeliver the requested (e.g., desired) EGR flow and/or blowthrough to theintake passage. In this way, reverse flow through the EGR passage,through the scavenge manifold, through the engine cylinders, and to theexhaust passage may be reduced while the electric compressor isoperating to boost the intake air and when the intake air pressure atthe compressor inlet (and where the EGR passage couples to the intakepassage) is greater than the scavenge manifold pressure.

FIG. 19 shows a graph 1900 of operating the split exhaust engine systemin the electric boost mode. Specifically, graph 1900 depicts anoperation state of an electric compressor (e.g., electric compressor 60shown in FIG. 1A) at plot 1902, a pressure in the scavenge exhaustmanifold (e.g., output from pressure sensor 34 shown in FIG. 1A,referred to herein as the scavenge manifold pressure) at plot 1904, apressure at the turbocharger compressor inlet (e.g., output frompressure sensor 31 shown in FIG. 1A, referred to herein as compressorinlet pressure) at plot 1906, an activation state of the scavengeexhaust valves (SVs) at plot 1908, and a position (open, closed, orsomewhere between fully open and fully closed) of the BTCC valve (e.g.,valve 54 shown in FIG. 1A) at plot 1910.

Prior to time t1 the electric compressor is off (e.g., not being drivenby the electric motor) and the scavenge manifold pressure is greaterthan the compressor inlet pressure. At time t1, the electric motorbegins driving the electric compressor and, as a result, the compressorinlet pressure (of the turbocharger compressor) begins increasing.However, since the scavenge manifold pressure is above the compressorinlet pressure between time t1 and time t2, the BTCC valve and SVs areadjusted based on a desired EGR flow amount and blowthrough level to theintake passage (e.g., based on engine operating conditions). At time t2,while the electric compressor is operating, the scavenge manifoldpressure decreases below the compressor inlet pressure. In response, theamount of opening of the BTCC valve is decreased. As shown in FIG. 19,the amount of opening of the BTCC valve is decreased but the BTCC valveis not fully closed. In alternate embodiments, the BTCC valve may befully closed or the SVs may be deactivated in response to the compressorinlet pressure increasing above the scavenge manifold pressure. At timet3, the scavenge manifold pressure increases above the compressor inletpressure. As a result, the amount of opening of the BTCC valve isreturned to a demanded level based on a desired EGR flow amount. In oneexample, as shown at time t3, this may include the fully open position.After time t3 (and after the BTCC valve is fully opened), the electriccompressor is no longer driven by the electric motor.

At time t4, the electric compressor is again being driven by theelectric motor. However, at this time, the compressor inlet pressure isless than the scavenge manifold pressure so the current position of theBTCC valve and the activation state of the SVs are maintained Inresponse to the compressor inlet pressure increasing above the scavengemanifold pressure at time t5, the SVs (of all the engine cylinders) aredeactivated. At time t5, electric compressor operation is stopped. Inresponse to the electric compressor no longer being driven by anelectric motor, the SVs are reactivated. Shortly thereafter, thecompressor inlet pressure decreases below the scavenge manifoldpressure.

In this way, the position of the BTCC valve and/or the activation stateof the scavenge exhaust valves may be controlled in response tooperation of an electric compressor, in order to reduce reverse fromthrough the EGR passage, to the exhaust passage, via the scavengeexhaust valves. A technical effect of adjusting a position of the BTCCvalve in response to an electric motor driving the electric compressor,based on the pressure in the scavenge exhaust manifold, is reducingreverse flow through the EGR passage to the exhaust passage via thescavenge exhaust while the compressor inlet pressure is greater than thescavenge manifold pressure, thereby increasing engine efficiency andreducing engine emissions.

FIG. 9 shows a method 900 for operating the engine system in acompressor threshold mode. Method 900 may continue from 421 of method400, as described above. The method begins at 902 by determining whetherconditions are met for mid-pressure EGR. In one example, the enginesystem may include a mid-pressure EGR passage (e.g., second EGR passage58 shown in FIG. 1A) coupled between a low-pressure EGR passage (e.g.,first EGR passage 50 shown in FIG. 1A) and an intake passage, downstreamof the turbocharger compressor. Flowing exhaust gases from the scavengemanifold to the intake passage via the mid-pressure EGR passage mayprovide mid-pressure EGR to the intake system of the engine. Since theexhaust gases are delivered downstream of the compressor via themid-pressure EGR passage, a temperature at the compressor and/orcompressor speed may be reduced while exhaust gases are directed to theintake from the scavenge exhaust manifold via the mid-pressure EGRpassage. In one example, the conditions for enabling mid-pressure EGR(e.g., conditions for flowing exhaust gases from the scavenge manifoldto the intake passage, downstream of the compressor via the mid-pressureEGR passage) may include one or more of EGR demand (e.g., desired EGRflow) being over a threshold level (e.g., high EGR demand), no EGRcooler being present in the EGR system (e.g., no EGR cooler in the firstEGR passage, such as EGR cooler 52 shown in FIG. 1A), no compressorbypass in the engine system (e.g., compressor recirculation passage 41shown in FIG. 1A), a temperature of the exhaust from the scavengeexhaust valves being above an upper threshold temperature, and/orcompressor flow conditions (e.g., if flow through the compressor isabove an upper threshold, EGR cannot be added to the compressor inletwithout degraded compressor operation/efficiency). If one or more of theconditions are met for enabling mid-pressure EGR, the method continuesto 904 to close the BTCC valve (e.g., valve 54 shown in FIG. 1A) andopen a mid-pressure EGR valve (e.g., valve 59 shown in FIG. 1A) disposedin the mid-pressure EGR valve. For example, opening the mid-pressure EGRvalve may include a controller sending a single to an actuator of themid-pressure EGR valve to fully open the mid-pressure EGR valve orincrease the amount of opening of the mid-pressure EGR valve (e.g., froma fully closed position). Closing the BTCC valve may include fullyclosing the BTCC valve such that no exhaust gases are routed to theintake passage upstream of the compressor. In an alternate embodiment,the method at 904 may include opening the mid-pressure EGR valve anddecreasing the amount of opening of the BTCC valve (but not fullyclosing) or maintaining the BTCC valve open. For example, in response tocompressor surge conditions, both the BTCC valve and mid-pressure EGRvalve may be opened. In yet another embodiment, the method at 904 mayinclude increasing the amount of opening of the mid-pressure EGR valvewhile decreasing the amount of opening of the BTCC valve, where theamount of increasing and decreasing the amount of opening of thesevalves is based on the compressor conditions (e.g., inlet temperature,outlet temperature, and rotational speed). For example, the controllermay determine a control signal to send to the actuators of the BTCCvalve and mid-pressure EGR valve based on a determination of thecompressor inlet temperature, compressor outlet temperature, and/orspeed of the compressor. These compressor conditions may be measured viaone or more sensors in the system (as shown in FIG. 1A), or determinedbased on operating conditions such as engine speed and load and/orcombustion air-fuel ratio. The controller may determine the desiredposition of the BTCC and mid-pressure EGR valves through a determinationthat directly takes into account the determined compressor conditions,such as increasing the amount of opening of the mid-pressure EGR valveand decreasing the amount of opening of the BTCC valve with increasingcompressor outlet temperature, increasing compressor speed, and/ordecreasing compressor inlet temperature (e.g., above/below thethresholds described above with reference to 420 in FIG. 4A). Thecontroller may alternatively determine the valve positions based on acalculation using a look-up table with the input being the compressorconditions and the output being the signal sent to the valve actuatorswhich corresponds to a valve position of the BTCC valve and mid-pressureEGR valve. After 904, the method ends. In alternate embodiments, themethod may continue from 904 to 906 to determine whether additionalengine actuator adjustments are desired to move the compressor away fromoperating at the operational thresholds.

Returning to 902, if conditions are not met for mid-pressure EGR oradditional actuator adjustments are desired to move the compressor awayfrom operating at or above the operational thresholds, the methodcontinues to 906. At 906, the method includes determining whethercondensate is forming at the compressor (e.g., at the compressor inlet).In one example, it may be determined that condensate is forming at thecompressor in response to an inlet temperature of the compressor (e.g.,a temperature of the gases entering the compressor inlet) being below afirst threshold temperature. In another example, it may be determinedthat condensate is forming, or expected to from, at the compressor whenambient humidity is above a threshold humidity value and/or when ambienttemperature is below a threshold temperature. If condensate is forming(or expected to from, in some examples) at the compressor, the methodcontinues to 908 to retard the exhaust valve cam (e.g., camshaft) timingto reduce the amount of EGR flowing from the scavenge manifold to theintake passage, upstream of the compressor, via the EGR passage.Retarding the exhaust valve cam timing may include retarding the timingof only the scavenge exhaust valves or both the scavenge and blowdownexhaust valves based on the valve timing hardware of the engine system.By retarding the timing of the scavenge exhaust valves, each scavengeexhaust valve may open and close later in the engine cycle (e.g., openat −90 crank angle degrees relative to TDC vs. approximately −135 crankangle degrees, as shown in FIG. 3B, as described above). As explainedabove with reference to FIGS. 1A-1B, various variable camshaft timing(VCT) system may be used to achieve the retarded timing of the scavengeexhaust valves (and possibly the blowdown exhaust valves). In oneexample, which may be the base engine system, both the scavenge exhaustvalves and the blowdown exhaust valves are controlled together via asingle camshaft system. Thus, retarding the exhaust cam results inretarding the timing of the scavenge exhaust valves and the blowdownexhaust valves (even though the opening and closing timing of thescavenge exhaust valves is different than the blowdown exhaust valves).In this way, the timing of the scavenge exhaust valves and blowdownexhaust valves are retarded by a same amount using the single camsystem. In another example, the VCT system for the exhaust valves mayinclude a CAM in CAM system where the timing of the scavenge exhaustvalves and blowdown exhaust valves may be varied independently from settimings. In yet another example, the VCT system for the exhaust valvesmay include a multi-air type system for the scavenge exhaust valves. Inthis system, the opening timing and lift for the scavenge exhaust valvesmay be individually controlled separately from the blowdown exhaustvalves (e.g., in this case, retarding only the scavenge exhaust valvetiming). In still another example, the VCT system for the exhaust valvesmay include an electric valve lift control on the scavenge exhaustvalves where the timing of the scavenge exhaust valves may be setseparately from the blowdown exhaust valves (e.g., retarded while thetiming of the blowdown exhaust valves is maintained).

At 910, the method includes determining whether the exhaust valve timing(of the scavenge exhaust valves) is at a maximum amount of retard. Forexample, the timing of the scavenge exhaust valves may only be retardedby a set number of crank angle degrees. Once the exhaust valve timingreaches the maximum amount of retard (e.g., a maximum amount ofadjustment), the exhaust valve timing may not be retarded any further.If the timing of the scavenge exhaust valves has not reached the maximumamount of retard, while the condensate is at the compressor (e.g., whenthe compressor inlet temperature is below the first thresholdtemperature), the method continues to 912 to continue retarding theexhaust cam timing of the scavenge exhaust valves. In some examples,this may include retarding the exhaust cam to the maximum amount ofretard. In other examples, this may include retarding the exhaust cam toan amount of retard that is less than the maximum amount of retard.

Alternatively at 910, if the maximum amount of retard for the exhaustcam has been reached and the scavenge exhaust valve timing cannot beretarded any further, the method continues to 914 to determine whetherthe intake cam of the intake valves may be advanced. Advancing thetiming of the intake valves may result in more overlap between an intakevalve and scavenge exhaust valve of each cylinder, thereby increasing anamount of blowthrough hot air recirculation to the compressor inlet.This may increase the compressor inlet temperature and reduce condensateformation at the compressor. The intake cam may be able to be advancedif it is not already advanced to its most advanced position (e.g., if itis not already at its maximum amount of advance). If the intake cam maybe advanced to advance the timing of the intake valves, the methodcontinues to 916 to advance the timing of the intake valves. This mayinclude actuating the intake cam (e.g., intake cam 151 shown in FIG. 1B)via an intake valve timing actuator (e.g., intake valve timing actuator101 shown in FIG. 1B) to advance the intake valve timing and thus openand close each intake valve sooner in the engine cycle. Otherwise, ifthe intake cam cannot be advanced any further, the method proceeds from914 to 918 to close the BTCC valve. For example, the method at 918 mayinclude fully closing the BTCC valve to block the flow of exhaust gasesfrom the scavenge manifold (e.g., scavenge exhaust manifold) to thecompressor inlet, thereby reducing low-pressure EGR and reducingcondensate formation at the compressor. The method at 918 may furtherinclude opening a scavenge manifold bypass valve (SMBV) arranged in abypass passage coupled between the scavenge manifold and the exhaustpassage (e.g., SMBV 97 in bypass passage 98 shown in FIG. 1A). Forexample, the controller may send a signal to an actuator of the SMBV toopen the SMBV in response to the BTCC valve closing. As a result, theexhaust gases from the scavenge manifold may be directed to the exhaustpassage while the BTCC valve is closed. In alternate embodiments, themethod at 918 may include decreasing the amount of opening of the BTCCvalve (without fully closing) and increasing the amount of opening ofthe SMBV (without fully opening). In some examples, the amount ofincreasing the amount of opening of the SMBV may be approximately thesame as (e.g., proportional to) the amount of decreasing the amount ofopening of the BTCC valve.

Returning to 906, if condensate is not forming or expected to form atthe compressor (e.g., if the compressor inlet temperature is not belowthe first threshold temperature), the method continues to 920 todetermine whether the compressor outlet temperature is greater than asecond threshold temperature. In one example, the compressor outlettemperature (e.g., a temperature of gases exiting the turbochargercompressor) may be measured via a temperature sensor positioneddownstream of or at the outlet of the compressor (e.g., temperaturesensor 43 shown in FIG. 1A). In other examples, the compressor outlettemperature may be estimated based on various other sensor outputs andengine operating conditions, such as the compressor inlet temperatureand a rotational speed of the compressor or an intake manifoldtemperature. If the compressor outlet temperature is greater than thesecond threshold temperature, the method continues to 922.

At 922, the method includes modulating the BTCC valve to reduce theamount of exhaust flow to the compressor inlet from the scavengemanifold, opening the SMBV, and/or opening the turbine wastegate (e.g.,wastegate 76 shown in FIG. 1A). In one example, modulating the BTCCvalve may include switching the BTCC valve between fully open and fullyclosed positions to reduce the amount of exhaust gas flow to thecompressor inlet via the EGR passage (compared to if the BTCC valve wereleft fully open) to a first level. Modulating the BTCC valve may includeincreasing the duration that the BTCC valve is closed compared to theduration that the BTCC valve is opened. The amount of modulating, or theaverage duration that the BTCC valve is closed, may be based on thecompressor outlet temperature and/or a desired EGR flow amount. Forexample, as the compressor outlet temperature increases further abovethe second threshold temperature, the BTCC valve may be closed for alonger duration and/or the average amount of time that the BTCC valve isclosed during a period of modulation may increase. In some examples, themethod at 922 may include fully closing the BTCC valve. In yet anotherexample, the method at 922 may include decreasing the amount of openingof the BTCC valve (e.g., to a position between fully open and fullyclosed, without modulating). The method at 922 may additionally includeopening the SMBV or increasing the amount of opening of the SMBV whilethe BTCC valve is closed or modulated between open and closed.Additionally or alternatively, the method at 922 may include opening theturbine wastegate while modulating the BTCC valve. Opening the turbinewastegate valve reduces the turbocharger speed and thus may reduce theload on the compressor.

The method continues to 924 to advance the intake cam of the intakevalves to reduce a pressure ratio across the compressor. For example,the intake cam may be advanced while the position of the BTCC valve isbeing modulated to reduce the EGR flow to the compressor inlet to thefirst level. The method then continues to 926 to retard the exhaust camto retard the exhaust valve opening timing (e.g., of at least thescavenge exhaust valves) to further decrease EGR. For example, retardingthe exhaust cam may result in the EGR flow to the compressor inlet to bereduced to a second level, lower than the first level. At 928, themethod includes increasing cold recirculation via opening the BTCCvalve. Since EGR flow is reduced because the exhaust valve (e.g.,scavenge exhaust valve) timing was retarded at 926, opening the BTCCvalve at 928 increases the flow of pressurized, colder air back to thecompressor inlet, thereby decreasing the compressor temperature.

Returning to 920, if the compressor outlet temperature is not greaterthan the second threshold temperature, the method continues to 930 todetermine whether the compressor is operating at an alternate compressorlimit (e.g., threshold). For example, the compressor speed (e.g.,rotational speed of the compressor) may be higher than a threshold speedwhich may result in degradation or reduced performance of thecompressor. If the compressor is operating at the alternate limit, suchas the compressor speed being higher than the threshold speed, themethod continues to 932 to close the BTCC valve and open the SMBV. Inone example, this may include fully closing the BTCC valve and fullyopening the SMBV. In another example, the method at 932 may includedecreasing the amount of opening of the BTCC valve (without fullyclosing) and increasing the amount of opening of the SMBV (without fullyopening). The amount of decreasing the amount of opening of the BTCCvalve and amount of increasing the amount of opening of the SMBV may bebased on a desired scavenge manifold pressure, where the desiredscavenge manifold pressure is based on the intake manifold pressure anda timing of the intake valves and exhaust valves. For example, theamount of overlap between when the scavenge exhaust valve and intakevalve are both open may determine the time available for blowthroughair, but the difference in pressure between the intake manifold (e.g.,MAP) and the scavenge manifold may determine the driving pressure forthe blowthrough flow. When MAP is greater than scavenge manifoldpressure, excess oxygen may flow to the exhaust passage via the scavengemanifold bypass passage. The desired driving pressure for theblowthrough flow may be based on desired oxygen levels in the exhaust,as discussed above with reference to FIGS. 2A-2B. Thus, as the intakemanifold pressure increases, the desired scavenge manifold pressure maydecrease for a set intake valve and exhaust valve timing and desiredblowthrough amount. For example, the controller may determine thedesired scavenge manifold pressure through a determination that directlytakes into account a determined intake manifold pressure and currentintake valve and exhaust vale timing and then determine correspondingpositions of the BTCC valve and SMBV that may achieve the desiredscavenge manifold pressure. As another example, the controller may makea logical determination (e.g., regarding a position of the BTCC valveand SMBV) based on logic rules that are a function of intake manifoldpressure, intake valve timing, and exhaust valve timing. The controllermay then generate a control signal that is sent to actuators of the BTCCvalve and SMBV.

At 934, the method includes advancing the scavenge exhaust valve timing(e.g., the opening timing of the scavenge exhaust valves) while the BTCCvalve is closed (or while the amount of opening of the BTCC valve isdecreased). For example, the amount of advance used for the scavengeexhaust valve opening may increase as the desired blowthrough amount tothe exhaust passage (e.g., to a second, downstream catalyst in theexhaust passage, as shown in FIG. 1A) decreases. The method thencontinues to 936 to increase the opening of the turbine wastegate,thereby decreasing turbocharger speed.

Alternatively at 930, if the compressor is not at an alternate limit,the method continues to 938 to maintain the turbine wastegate closed. Insome embodiments, the default position of the turbine wastegate may beclosed. The wastegate may then only be opened at high turbochargerspeeds. The method at 938 may include returning to method 400 of FIGS.4A-4B.

FIG. 20 shows a graph 2000 of operating the split exhaust engine systemin the compressor threshold mode. Specifically, graph 2000 depictsengine load at plot 2002, EGR demand (e.g., desired EGR flow to theintake passage) at plot 2004, compressor outlet temperature at plot2006, compressor inlet temperature at plot 2008, compressor (e.g.,turbocharger) speed at plot 2009, a position of the turbine wastegate atplot 2010, a position of the BTCC valve at plot 2012, a position of themid-pressure EGR valve at plot 2014, a position of the SMBV at plot2016, an intake valve timing of the intake valves at plot 2018, and anexhaust valve timing of the scavenge exhaust valves at plot 2020. In anembodiment where the scavenge exhaust valves and blowdown exhaust valvesare controlled via a same cam system, the exhaust valve timing at plot2020 may be the timing for both the scavenge exhaust valves and theblowdown exhaust valves. Though the valve positions may be shown as openand closed in FIG. 20, in alternate embodiments, the valves may beadjusted into a plurality of positions between fully open and fullyclosed.

Prior to time t1, compressor inlet temperature is above the firstthreshold temperature T1, compressor outlet temperature is below thesecond threshold temperature T2, and compressor speed is below thethreshold speed S1. Thus, the BTCC valve is open, the mid-pressure EGRvalve is closed, and the relief pipe valve is closed. The intake andexhaust valve timings are also at their default timings (as shown bydefault line D1) for best fuel economy prior to time t1. At time t1, thecompressor inlet temperature decreases below the first thresholdtemperature T1, thereby indicating that condensate may be forming at thecompressor. Also at this time, the EGR demand is relatively high, thus,in response to the compressor inlet temperature being below the firstthreshold temperature T1 while the EGR demand is relatively high, theBTCC valve is closed and the mid-pressure EGR valve is opened. This mayreduce low-pressure EGR flow to the compressor inlet, thereby reducingcondensate formation. At time t2, the compressor inlet temperatureincreases above the first threshold temperature T1, thus, the BTCC valveis reopened and the mid-pressure EGR valve is closed shortly after timet2.

At time t3, the compressor outlet temperature increases above the secondthreshold temperature T2 while EGR demand is at a relatively lower level(e.g., lower than at time t1). In response to these conditions, the BTCCvalve is modulated to reduce EGR flow and the SMBV is correspondinglymodulated to be open when the BTCC valve is closed. Additionally,between time t3 and time t4, the intake valve timing is advanced and theexhaust valve timing is retarded. At time t4, in response to thecompressor outlet temperature decreasing below the second thresholdtemperature T2, the BTCC valve is opened and the SMBV is closed and theintake and exhaust valve timings are returned to their default positionsfor best fuel economy.

At time t5, the compressor inlet temperature again decreases below thefirst threshold temperature T1 while the EGR demand is at a lower level(compared to the higher EGR demand level at time t1). Thus, the exhaustvalve timing is retarded just after time t5 to reduce EGR flow to thecompressor inlet. At time t6, the exhaust valve timing reaches themaximum amount of retard (e.g., cannot be retarded any further). Inresponse to reaching this maximum level, the intake valve timing isadvanced. At time t7, the compressor inlet temperature increases abovethe first threshold temperature and, in response, the intake and exhaustvalve timings are returned to their default timings.

At time t8, the compressor speed increases above the threshold speed S1.In response to this increase in compressor speed, the BTCC valve isclosed and the SMBV is opened. Also after time t8, the scavenge exhaustvalve timing is advanced and the turbine wastegate is opened. After theturbine speed decreases back below the threshold speed S1 at time t9,the BTCC valve is opened, the SMBV closed, and the scavenge exhaustvalve timing is returned to the default timing. In this way, the intakevalve timing, exhaust valve timing of the scavenge exhaust valves, and aposition of the BTCC valve (and in some examples, the SMBV) may beadjusted in coordination in response to a condition at the compressor(e.g., the compressor reaching one or more operational thresholds, asdescribed above). For example, as shown at time t3, the BTCC valve ismodulated to reduce EGR flow to a first level and the exhaust valvetiming is retarded to decrease the EGR flow to a lower, second level. Atthe same time, intake valve timing is advanced to reduce the pressureratio across the compressor. As another example of adjusting the intakevalve timing, exhaust valve timing, and BTCC valve timing incoordination with one another, as shown at times t5 to t7, the scavengeexhaust valve timing is retarded and upon hitting its maximum amount ofretard while the compressor inlet temperature is still below the firstthreshold temperature, the intake valve timing is advanced. A technicaleffect of adjusting the intake valve timing, exhaust valve timing of thescavenge exhaust valves, and the position of the BTCC valve, incoordination with one another, is to reduce EGR flow to the compressorinlet and thus reduce condensate formation at the compressor, reduce thecompressor outlet temperature, and/or reduce the compressor speed,thereby reducing degradation of the compressor. In another embodiment,as shown at time t1, in response to the compressor inlet temperaturebeing below the threshold inlet temperature, the mid-pressure EGR valvemay be opened to direct exhaust from the scavenge exhaust valves to theintake passage, downstream of the compressor. A technical effect ofrouting exhaust from the scavenge exhaust valves to the intake passage,downstream of the compressor, in response to a condition of thecompressor, is to reduce EGR flow to the compressor inlet, therebyreducing condensate formation at the compressor, increasing thecompressor outlet temperature, and reducing compressor speed. As aresult, compressor degradation may be reduced. In yet anotherembodiment, as shown at times t3 and t8, the BTCC valve may be closed(or modulated between open and closed) while the SMBV is correspondinglyopened (or modulated) to reduce EGR flow to the compressor inlet andinstead direct the exhaust gases from the scavenge manifold to theexhaust passage. A technical effect of decreasing gas flow from thescavenge exhaust manifold to the intake passage, upstream of thecompressor, in response to an engine operation condition (such as acompressor outlet temperature being greater than a threshold outlettemperature and/or a compressor speed being greater than a thresholdspeed) and, in response to the decreasing gas flow, increasing gas flowfrom the scavenge exhaust manifold to the exhaust passage via thescavenge manifold bypass passage is reducing compressor degradationwhile also reducing pressures in the scavenge exhaust manifold andtrapping of residual gases within the cylinders.

FIG. 10 shows a method 1000 for operating the engine system in abaseline BTCC mode. Method 1000 may continue from 430 of method 400, asdescribed above. Method 1000 begins at 1002 by setting the intake camtiming of the intake valves and the exhaust cam timing of the scavengeexhaust valves and blowdown exhaust valves for best fuel economy. Forexample, the timing of the exhaust valves and intake valves may be setfor the best achievable brake specific fuel consumption (BSFC) at thecurrent engine operating conditions. In one example, this may includesetting the timing of the scavenge exhaust valve, blowdown exhaustvalve, and intake valve of each cylinder at the timings shown in FIG.3A, as described above. In some embodiments, the timing of the exhaustvalves and intake valves may be adjusted slightly from the timings shownin FIG. 3A based on engine speed and load. For example, the intaketiming may be adjusted to full retard at lighter engine loads andadvanced when the engine is boost limited or there is a request forincrease blowthrough to reduce knock. In another embodiment, exhaustvalve timing may be adjusted so that the exhaust valves open earlier asengine speed increases. The exhaust valve timing may then be retarded asboost decreases (e.g., at low engine speed and high engine loadconditions) or when engine speed is high and the EGR temperature isgreater than a threshold temperature.

At 1004, the method includes determining whether engine torque output isat a demanded level. The demanded torque level may be a vehicle operatortorque demand determined based on a position of an accelerator pedal ofthe vehicle, in one example. In one example, the controller maydetermine the demanded torque in response to a pedal position signalreceived from a pedal position sensor of the accelerator pedal. Iftorque is not at the demanded level, the method continues to 1006 tooptimize the cam timing and BTCC valve position for the demanded torque.As one example, this may include restricting the scavenge exhaust valveflow to increase the torque output and modifying the amount ofrestricting based on a surge threshold of the turbocharger compressor.For example, restricting the scavenge exhaust valve flow may includeretarding the cam timing of the scavenge exhaust valves to reduce EGRflow. In yet another example, this may include alternatively oradditionally retarding the cam timing of the intake valves to reduceblowthrough from the scavenge exhaust valves to the intake passage.Further, modifying the amount of restricting the scavenge exhaust valveflow may include decreasing the amount of restricting as compressoroperation (e.g., flow rate and pressure drop across the compressor)approaches the surge threshold or surge line. In yet another example,the method at 1006 may additionally or alternatively include restrictingthe amount of opening of the BTCC valve (e.g., closing or decreasing theamount of opening).

If the engine torque output is at the demanded level, the methodcontinues to 1008 to measure the oxygen content and pressure of gases inthe scavenge manifold (e.g., scavenge exhaust manifold 80 shown in FIG.1A). In another embodiment, the method at 1008 may additionally oralternatively include measuring the oxygen content and/or pressure ofgases in the exhaust runner of each scavenge exhaust valve. For example,the method at 1008 may include obtaining pressure and oxygen contentmeasurements from one or more pressure sensors and oxygen sensorsdisposed in the scavenge manifold and/or scavenge exhaust valve runners(e.g., pressure sensor 34, oxygen sensor 36, and/or oxygen sensors 38shown in FIG. 1A).

As described above, both exhaust gases (e.g., EGR, after the cylinderfires via combusting an air-fuel mixture in the cylinder) andblowthrough air (during an overlap period between opening of the intakevalve and scavenge exhaust valve) may be expelled into the scavengemanifold from the engine cylinders via the scavenge exhaust valves.Further, each scavenge exhaust valve of each engine cylinder may expelEGR and blowthrough air at different times than the other enginecylinders (e.g., based on a set firing order of the cylinders during oneengine cycle). As used herein, an engine cycle refers to a period duringwhich each engine cylinder fires once, in the cylinder firing order. Forexample, if the cylinder firing order includes firing the cylinders inthe following order: cylinder 1, cylinder 2, cylinder 3, and thencylinder 4, then the scavenge exhaust manifold may receive four separatepulses of EGR and blowthrough from each cylinder, in the cylinder firingorder, during each engine cycle. As such, at 1010, the method includesestimating blowthrough (BT, e.g., the amount of non-combusted gasesentering the scavenge manifold from the scavenge exhaust valve during anoverlap period between the intake valve and scavenge exhaust valve ofeach cylinder) and EGR (e.g., combusted exhaust gases). Estimating BTand EGR may include estimating a BT amount and EGR amount expelled intothe scavenge exhaust manifold for each cylinder and/or estimating atotal amount of BT and EGR entering the intake passage for all cylindersduring a single engine cycle (e.g., total BT and EGR amount for fourcylinders in a four cylinder engine, or as many cylinders that haveactivated scavenge exhaust valves). In a first embodiment of the methodat 1010, the method at 1011 may include estimating the BT and EGR amountbased on crankshaft angle (e.g., engine position) and scavenge manifoldpressure (e.g., based on an output of a pressure sensor in the scavengemanifold). In a second embodiment of the method at 1010, the method at1013 may include estimating the BT and EGR amount based on crankshaftangle (or a corresponding time of opening and closing the intake valveand scavenge exhaust valve of each cylinder) and the oxygen content ofthe scavenge manifold (e.g., based on an output of an oxygen sensor inthe scavenge manifold or in each scavenge exhaust valve runner).

FIG. 21 shows a graph 2100 of changes in scavenge manifold pressure andoxygen content over a single engine cycle that includes firing of fourcylinders (e.g., cylinders 1-4 shown in FIG. 21). Specifically, graph2100 illustrates an engine position along the x-axis in crank angledegrees (CAD) for a complete engine cycle (e.g., from −360 CAD to 360CAD) where four cylinders of a representative four-cylinder engine fire(e.g., such as the engine shown in FIGS. 1A-1B). For each cylinder, atiming, lift, and duration of opening (relative to the engine position)of the intake valve (IV), scavenge exhaust valve (SV), and blowdownexhaust valve (BDV) are shown. Plot 2102 depicts the cylinder valveevents for a first engine cylinder, cylinder 1; plot 2104 depicts thecylinder valve events for a second engine cylinder, cylinder 2; plot2106 depicts the cylinder valve events for a third engine cylinder,cylinder 3; and plot 2108 depicts the cylinder valve events for a fourthengine cylinder, cylinder 4. Changes in the measured scavenge manifoldpressure over the engine cycle are shown at plot 2110 and changes in themeasured scavenge manifold oxygen content are shown at plot 2112. Themeasured scavenge manifold oxygen content may also represent an air-fuelratio of the gases entering the scavenge exhaust manifold from the SVs.

As shown in graph 2100, each time a SV of one of the cylinder opens,there is a positive pulse in the scavenge manifold pressure and anegative pulse in the scavenge manifold oxygen content. For example,when a SV opens (e.g., at −90 CAD for cylinder 2), combusted exhaustgases are expelled into the scavenge manifold. While the same SV is openand upon opening of an IV of the same cylinder (e.g., overlap period, asindicated by 2114 for cylinder 2), blowthrough air is expelled into thescavenge manifold. Thus, an increase in scavenge manifold pressureoccurs upon opening of the SV and the scavenge manifold oxygen contentdecreases due to the combusted exhaust gases entering the scavengemanifold. While the SV is open and before opening of the IV, thescavenge manifold oxygen content represents an air-fuel ratio of thecombusted exhaust gases (which may be richer). Then, the scavengemanifold content increases again as the blowthrough air (e.g., thatdoesn't include combusted gases and thus is more oxygen rich thanexhaust gases) enters the scavenge manifold. While both the SV and theIV are open at the same time for each cylinder, the scavenge manifoldoxygen content represents an air-fuel ratio of the blowthrough air whichis leaner than the combustion gases.

Thus, by correlating the pulses in scavenge manifold pressure and/oroxygen content to CAD, the pressure and/or oxygen changes due to exhaustgases and blowthrough air for each cylinder may be determined anddifferentiated between. By observing the size (e.g., magnitude) of thesepulses over the known period (e.g., CAD and firing order) of expellingexhaust gases or blowthrough air into the scavenge manifold, the amountof EGR and blowthrough air flowing to the intake passage via thescavenge manifold may be determined for each cylinder or for each enginecycle (e.g., by summing the pulses). As another example, estimatingblowthrough and/or EGR flow from the scavenge manifold oxygen contentmay include measuring (via an oxygen sensor) a transition between acombustion air-fuel content of the gases (e.g., combustion gases)expelled from each SV (e.g., the valleys, or low points, of plot 2112)and a leaner air-fuel content of gases (e.g., blowthrough air) expelledfrom each SV (e.g., the peaks, or high points, of plot 2112). Thetransition, or change between a peaks (e.g., maximum) and valley (e.g.,minimum) of the oxygen sensor output, for each cylinder, may beindicative of the EGR and blowthrough air amount exiting the SV for eachcylinder and flowing to the intake For example, the transition mayinclude an increase in the oxygen level of the blowthrough air expelledfrom the SVs. The increase in the oxygen level may be an increase from alower, first level of oxygen (at the valleys) to a higher, second levelof oxygen (at the peaks). The transition between the combustion air-fuelratio content of the expelled gases and the leaner air-fuel content ofthe gases may be determined, on a cylinder to cylinder basis, todetermine the EGR flow and blowthrough amounts for each cylinder.Additionally, the total amount of the blowthrough air flowing to theintake passage from the scavenge manifold during a single engine cyclemay be determined based on the second level of oxygen for each SV ofeach cylinder.

Returning to 1010 of FIG. 10, in this way, the BT amount and EGR amountmay be determined based on an output of a pressure sensor and/or oxygensensor positioned in the scavenge manifold (or scavenge exhaust valvesrunners) that is correlated to crank angle degree (e.g., engineposition). As one example, the controller may determine the BT amountfor a first cylinder based on the received output of the pressure sensorbetween a time of opening the intake valve of the first cylinder and atime of closing the scavenge exhaust valve of the first cylinder. Thecontroller may repeat this process for each engine cylinder and then sumall values to determine a total BT amount to the intake passage for acompete engine cycle. As another example, the controller may determinethe EGR flow amount for the first cylinder based on the received outputof the pressure sensor between a time of opening the scavenge exhaustvalve of the first cylinder and a time right before opening the intakevalve of the first cylinder (e.g., the time up until the intake valveopens and, thus, before BT air enters the scavenge manifold). The sameprocess may be performed using the output of the oxygen sensor insteadof the pressure sensors. As one example, the controller may make alogical determination regarding the amount of EGR or BT in the scavengemanifold based on logic rules that are a function of the pressure (oroxygen content) of the scavenge manifold (for the set BT or EGR period,as discussed above, for each cylinder).

At 1012, the method includes adjusting the BTCC valve (e.g., adjusting aposition of the BTCC valve), scavenge exhaust valve (SV) timing, intakevalve (IV) timing, and/or SMBV (e.g., adjusting a position of the SMBV)based on the estimated blowthrough and EGR flow amounts (as determinedat 1010), desired blowthrough and EGR flow amounts, boost level (e.g.,boost pressure downstream of turbocharger compressor), and currentpositions and timings of each of the above-listed valves. As oneexample, the BTCC valve may be opened in response to the engine beingboosted (e.g., with the turbocharger compressor operating and resultingin MAP greater than atmospheric pressure). As another example, if moreof less EGR flow or blowthrough to the intake passage via the scavengemanifold and EGR passage is desired relative to the estimated levels(estimated at 1010), the controller may adjust the positions or timingsof one or more of the BTCC valve, SV, IV, and SMBV to achieve thedesired EGR flow and blowthrough flow. Details on adjusting the BTCCvalve, SMBV, and SV timing to achieve desired EGR and blowthrough floware described further below with reference to FIGS. 12-13. Further,adjusting the valve positions and timings at 1012 may include adjustingthe valve positions and/or timings relative to the positions and timingsof one another. For example, if the BTCC valve is closed, and thedesired scavenge manifold pressure is lower than the currently measuredscavenge manifold pressure, the method at 1012 may include opening orincreasing the amount of opening of the SMBV to decrease the scavengemanifold pressure.

In another example of the method at 1012, the scavenge manifold pressureat certain SV timings may change the control of the BTCC valve, SMBV,and/or intake valve. For example, the SV timing may be adjusted based onthe measured scavenge manifold pressure. In one example, in response tothe measured scavenge manifold pressure being greater than the desiredscavenge manifold pressure, the method may include retarding the SVtiming to decrease the scavenge manifold pressure. The desired scavengemanifold pressure may be determined based on (e.g., as a function of)one or more of intake manifold pressure, exhaust pressure, and/or boostconditions (e.g., whether the engine is boosted or not). Further, inresponse to adjusting the SV timing based on the measured pressure andin response to the scavenge manifold pressure, the positions of the BTCCvalve and/or SMBV may be adjusted. For example, after adjusting the SVtiming, the position of the SMBV may be adjusted to maintain thescavenge manifold pressure at the desired scavenge manifold pressure(based on engine operating conditions) and the position of the BTCCvalve may be adjusted to maintain EGR flow at a desired EGR flow (e.g.,based on engine operating conditions such as engine load, knock, andcompressor operating conditions such as temperature and speed).

The method proceeds to 1014 to close the charge motion control valves(e.g., CMCVs 24 shown in FIG. 1A) positioned in at least one intakerunner of each cylinder. As one example, closing the CMCVs may includethe controller actuating a valve actuator of the CMCVs to move the CMCVsinto the closed position that restricts airflow entering the cylindervia the intake valves of the intake runners that the CMCVs are coupledwithin. For example, the closed position may include when the CMCVs arefully activated and the valve plate of the CMCVs may be fully tiltedinto the respective intake runner (e.g., port), thereby resulting inmaximum air charge flow obstruction. This may reduce short circuiting ofair from the intake valve directly to the SV without fully scavengingexhaust gases from inside the cylinders. As a result of closing theCMCVs while operating in the baseline BTCC mode, more exhaust gasscavenging may result, thereby increasing engine performance and torqueoutput during subsequent cylinder combustion events.

At 1016, the method includes determining whether conditions are met forrunning a valve diagnostic for one or more of the BTCC valve, SMBV, orSVs. In one example, the conditions for running the valve diagnostic mayinclude one or more of a duration passing since a previous valvediagnostic, a duration of engine operation, and/or a number of enginecycles. For example, the valve diagnostic may be run at regularintervals (e.g., after a set duration of engine operation or a setnumber of engine cycles), after each shutdown event (e.g., upon enginerestart), or in response to a diagnostic flag set at the controller. Forexample, a diagnostic flag may be set if a measured scavenge manifoldpressures is a threshold amount different than expected based on thecurrent valve positions and timings of the BTCC valve, SMBV, and/or SVs.If conditions are met for running the valve diagnostic, the methodproceeds to 1018 to run the valve diagnostic and diagnose a position ortiming of the BTCC valve, SMBV, and SVs based on scavenge manifoldpressure. Details on running this diagnostic routine are described infurther detail below with reference to FIG. 11. Alternatively at 1016,if conditions are not met for running the valve diagnostic, the methodproceeds to 1020 to not run the diagnostic and instead continue engineoperation at the current valve positions/timings Method 1000 then ends.

In this way, the BTCC valve, SV timing, IV timing, and/or SMBV may beadjusted based on an estimate of blowthrough and EGR flow that isdetermined based on a scavenge manifold pressure or oxygen contentmeasurement (or estimate). As one example, a method includes adjustingan amount of opening overlap between the intake valves and the scavengeexhaust valves (e.g., via advancing or retarding the SV and IV timing,as explained above) responsive to a transition from an estimatedcombustion air-fuel content to a leaner air-fuel content of theblowthrough air on a cylinder to cylinder basis. As explained above, foreach cylinder, there may be a transition from the estimated combustionair-fuel content to the leaner air-fuel content corresponding to a SVopening event for each cylinder. A technical effect of adjusting theopening overlap responsive to this transition is delivering the desiredamount of blowthrough to the intake passage and thus, increasing engineefficiency and reducing engine knock. As another example, a methodincludes adjusting the BTCC valve, the SMBV, SV timing, and/or IV timingbased on measured pressure in the scavenge exhaust manifold. A technicaleffect of adjusting these valves and/or valve timings based on thescavenge manifold pressure increasing the accuracy of the control of theblowthrough and EGR flow amounts to the intake passage, therebyincreasing engine efficiency, reducing engine emissions, and reducingengine knock.

Turning to FIG. 11, a method 1100 for diagnosing one or more valves ofthe split exhaust engine system based on scavenge manifold pressure isshown. Method 1100 may continue from 1018 of method 1000, as describedabove. The method begins at 1102 by determining an expected pressuredrop across each of the BTCC valve and the SMBV and determining theexpected timing of the scavenge exhaust valves (SVs). As one example,the expected pressure drop (e.g., difference) across the BTCC valve andthe SMBV may be determined based on a commanded position of the BTCCvalve and the SMBV and additional engine operating conditions. Forexample, the commanded position of the valves may include a fully openposition, fully closed position, or one of a plurality of positionsbetween the fully open and fully closed positions. In the case of theexpected pressure drop across the BTCC valve, the additional engineoperating conditions may include a pressure in the intake passage,upstream of the compressor (e.g., where the EGR passage couples to theintake passage), atmospheric pressure (e.g., if there is no electriccompressor upstream of the compressor or the electric compressor is notoperating), a position of the SMBV (e.g., open or closed), an exhaustpressure in the exhaust passage where the scavenge manifold bypasspassage couples to the exhaust passage, and/or a timing of the SVs. Asone example, the controller may determine the expected pressure dropacross the BTCC valve based on a look-up table stored in memory of thecontroller, where the look-up table includes one or more of thecommanded BTCC valve position, intake pressure, atmospheric pressure,exhaust pressure, SMBV position, and SV timing as inputs and theexpected pressure drop across the BTCC valve as the output. In anotherexample, the controller may determine the expected pressure dropaccording to a relationship stored in the memory of the controller thatis a function of the commanded BTCC valve position, intake pressure,atmospheric pressure, exhaust pressure, SMBV position, and/or SV timing.Similarly, the controller may determine the expected pressure dropacross the SMBV based on the commanded SMBV position and engineoperating conditions which may include one or more of a position of theBTCC valve, a timing of the SVs, and the exhaust pressure in the exhaustpassage where the scavenge manifold bypass passage couples to theexhaust passage (e.g., using look-up tables or stored relationships, asexplained above). In one example, the exhaust pressure in the exhaustpassage where the scavenge manifold bypass passage couples to theexhaust passage may be a pressure measured via a pressure sensordisposed in the exhaust passage, such as pressure sensor 96 shown inFIG. 1A. In another example, the intake pressure where the EGR passagecouples to the intake passage may be measured via a pressure sensordisposed in the intake passage upstream of the compressor, such aspressure sensor 31 shown in FIG. 1A. The expected timing of the SVs maybe the currently set (or last commanded) timing of the SVs. For example,the controller may look-up or determine the last commanded, or baseline,timing for the SVs and use that as the expected SV timing.

At 1104, the method includes determining the actual pressure dropsacross the BTCC valve and across the SMBV and determining the actualtiming of the SVs based on a measured pressure in the scavenge manifold.As one example, the scavenge manifold pressure may be measured via apressure sensor disposed within the scavenge manifold (e.g., pressuresensor 34 shown in FIG. 1A). The controller may receive the time varyingsignal of the scavenge manifold pressure sensor and then determineeither an instantaneous or average scavenge manifold pressure (e.g.,averaged over an engine cycle or a plurality of engine cycles). As oneexample, the actual pressure drop across the BTCC valve may bedetermined based on the output of the scavenge manifold pressure sensorand atmospheric pressure (or based on an output of a pressure sensordisposed in the intake passage, where the EGR passage couples to theintake passage, upstream of the compressor). For example, the controllermay determine the actual pressure drop across the BTCC valve based on alook-up table stored at the controller, where the look-up table includesthe measured scavenge manifold pressure and atmospheric (or intakepressure) as inputs and the actual BTCC valve position as the output.Similarly, the controller may determine the actual pressure drop acrossthe SMBV based on the output of the pressure sensor positioned in thescavenge manifold and an output of a pressure sensor positioned in theexhaust passage, at an outlet of the scavenge manifold bypass passage(e.g., pressure sensor 96 shown in FIG. 1A). Additionally, thecontroller may determine the actual timing (e.g., opening timing) of theSVs based on a spike in the output of the scavenge manifold pressuresensor during a single engine cycle. For example, as described above inreference to FIG. 21, the pressure signal of the scavenge manifoldpressure sensor may pulse (or spike) each time a SV opens. Thecontroller may correlate this pulse to the CAD (or engine position) atwhich the pulse occurs and thus determine the opening and closing timingof the SVs.

The method then proceeds to 1106 to determine whether an absolute valueof a difference between the actual pressure drop or timing determined at1104 and the expected pressure drop or timing determined at 1102 isgreater than a threshold difference. The method at 1106 may includedetermining this difference for each of the BTCC valve, SMBV, and theSVs. The threshold difference may be a difference that is non-zero andindicative of the valves being in a different position than desired orat a different timing than desired. For example, this difference may bea difference that indicates that the BTCC valve is mis-positioned (e.g.,opened instead of closed or closed instead of opened). In anotherexample, this difference may be a difference that indicates that thetiming of the SVs is a threshold amount of CADs different than desired(or commanded) These differences may result in degraded engineperformance, such as reduced torque output, increased emissions, and/ordegradation of the turbocharger or emission control devices.

If the absolute value of the difference between the actual pressure dropor timing and the expected pressure drop or timing is not greater than athreshold difference, the method continues to 1110 to continue operatingthe valves at the set positions and/or timings based on the currentengine operating conditions (e.g., according to method 400 describedabove with reference to FIGS. 4A-4B). For example, if the differencebetween the actual pressure drop or timing and the expected pressuredrop or timing is not greater than the threshold difference, the valvesmay not be degraded and they may be in their commanded or set positions.

Alternatively at 1106, if the difference between the actual pressuredrop or timing and the expected pressure drop or timing is greater thanthe threshold difference, the method continues to 1108 to adjust thecommanded position/timing of the identified valve(s), indicatedegradation of the identified valve(s), and/or adjust an alternate valveto deliver the desired EGR and blowthrough amounts to the intakepassage. As introduced above, method 1100 may be performed for one ormore of or each of the SVs, BTCC valve, and SMBV. As such, the methodproceeds to 1108 to perform the above-described actions for any and allof the valves for which the difference between the actual pressure dropor timing and the expected pressure drop or timing is greater than thecorresponding threshold difference. In one example, the controller mayindicate degradation of the identified valve(s) by setting a diagnosticflag and/or alerting a vehicle operator that the identified valve(s)need to be serviced or replaced (e.g., via an audible or visual signal).In another example, the controller may actuate the identified valve(s)into the desired (e.g., originally commanded) positions or timings. Forexample, if the BTCC valve is diagnosed as being mispositioned, themethod at 1108 may include actuating the valve into the desired position(e.g., open or closed) and then the controller may re-run the diagnosticto see if the BTCC valve was moved into the desired position. In anotherexample, if the identified valve are the SVs, the method at 1108 mayinclude further retarding the SV timing, past a desired or previouslycommanded level, if the actual timing is more advanced that the desiredtiming. In this way, adjusting the valve positions or timings at 1108may include compensating for the difference determined at 1106 and thusresult in achieving a desired valve position or timing. In yet anotherexample, and as explained in further detail below with reference toFIGS. 12-13, the method at 1108 may include adjusting an alternatevalve, other than the identified valve, (e.g., one of the non-degradedor correctly positioned valves) to deliver the desired EGR orblowthrough flow. For example, if the BTCC valve is identified as beingmispositioned based on the difference determined at 1106, the method mayinclude adjusting the timing of the SVs to deliver the desired EGR andblowthrough and not adjusting the BTCC valve. In another example, inresponse to the difference between the actual pressure drop and theexpected pressure drop across the BTCC being greater than the thresholddifference, the EGR flow to the intake passage may be adjusted to thedesired level via adjusting the position of the SMBV and/or the timingof the SVs and not by adjusting the position of the BTCC valve. In yetanother example, in response to determining that the SMBV ismispositioned, the controller may instead adjust the BTCC valve todeliver the desired EGR flow and blowthrough. In yet another example,the method at 1108 may include adjusting the flow of exhaust gases fromthe SVs to the intake passage via adjusting only the BTCC valve and notthe timing of the SVs in response to the actual opening timing of theSVs being a threshold amount different than the expected timing. In thisway, the desired EGR flow and blowthrough may still be delivered to theintake passage, even if one or more of the above-described valves isdegraded or mispositioned.

In this way, a position of one or more of the BTCC valve and SMBV,and/or a timing of the SVs, may be diagnosed based on an output of apressure sensor positioned in the scavenge exhaust manifold. The valvethat is diagnosed as being degraded or mispositioned may then becommanded into a different position and/or an alternate valve may beadjusted to achieve desired operating conditions (such as a desired EGRflow or pressure in the first exhaust manifold). Thus, a technicaleffect of diagnosing the BTCC valve, SMBV, and/or SVs based on scavengemanifold pressure is increasing an ease of determining valve degradation(e.g., determining when a valve may need to be serviced or replaced) andbeing able to deliver the desired EGR flow or blowthrough amount to theintake passage, even when one or more of these valves is mispositionedor degraded, by adjusting an alternate valve. In this way, engineefficiency and fuel economy may be maintained, even when one or morevalves are diagnosed as being degraded or mispositioned.

In embodiments where a hot pipe valve or mid-pressure EGR valve areincluded in the split exhaust engine system (e.g., hot pipe valve 32 andmid-pressure EGR valve 59 shown in FIG. 1A), method 1100 may furtherinclude diagnosing the positions of these valves, similar to diagnosingthe BTCC valve and SMBV, as disclosed above.

Turning now to FIG. 12, a method 1200 for controlling EGR flow andblowthrough air to the intake passage from the scavenge manifold viaadjusting operation of one or more valves of the engine system is shown.Method 1200 may continue from 1012 of method 1000 or from 1108 of method1100, as described above. For example, method 1200 may run in responseto changing engine operating conditions (which may include changes invalve positions, cylinder valve timings, system pressures, etc.) thatresult in a change in the desired EGR flow amount or rate or the desiredblowthrough flow amount or rate to the intake passage from the scavengeexhaust manifold (e.g., scavenge manifold). Method 1200 may additionallyor alternatively continue from one or more of the other methodsdescribed herein (e.g., with reference to FIGS. 4-10) that describechanging (e.g., increasing or decreasing) the EGR flow of blowthroughflow to the intake passage.

Method 1200 begins at 1202 by determining whether there is a request toincrease EGR. In one example, there may be a request to increase EGR(e.g., from scavenge manifold 80, via EGR passage 50, to the intakepassage, as shown in FIG. 1A) when an estimated EGR flow rate is lessthan a desired EGR flow rate (as described above with reference to FIG.10). In another example, there may a request to increase EGR followingan engine cold start where the BTCC valve was closed or at leastpartially closed. Further, a request to increase EGR may be generated inresponse to an outlet temperature of the turbocharger compressordecreasing below a threshold outlet temperature, an inlet temperature ofthe turbocharger compressor increasing above a threshold inlettemperature, and/or a speed of the compressor decreasing below athreshold speed. If there is a request to increase EGR (e.g., increasethe amount of exhaust gas flow from the engine cylinders to the intakepassage via the scavenge exhaust valves (SVs) and the scavengemanifold), the method proceeds to 1204 to adjust one or more engineactuators to increase EGR flow from the scavenge manifold to the intakepassage. Increasing EGR at 1204 may include one or more of opening theBTCC valve at 1206, advancing the timing (e.g., opening and closingtiming) of the SVs at 1208, and closing the SMBV at 1210. Opening theBTCC valve (e.g., valve 54 shown in FIG. 1A) may include the controllersending a signal to an actuator of the BTCC valve to fully open orincrease the amount of opening of (but not fully opening) the BTCCvalve. Similarly, closing the SMBV (e.g., SMBV 97 shown in FIG. 1A) mayinclude the controller sending a signal to an actuator of the SMBV tofully close or decrease the amount of opening of (but not fully closing)the SMBV. Further, advancing the SV timing may include the controllersending a signal to an actuator of the SVs (e.g., SVs 6 shown in FIG.1A) to advance the timing of the SVs alone or all the exhaust valves(e.g., when the SVs and BDVs are controlled via a same actuator and camtiming system). The method at 1204 may include selecting which one ormore of the adjustments at 1206, 1208, and 1210 to utilize to increaseEGR to the desired level based on engine operating conditions, asdescribed further below with reference to FIG. 13.

If there is not a request to increase EGR at 1202, the method continuesto 1212 to determine if there is a request to decrease EGR. In oneexample, there may be a request to decrease EGR (e.g., from scavengemanifold 80 via EGR passage 50, as shown in FIG. 1A) when an estimatedEGR flow rate is greater than a desired EGR flow rate (as describedabove with reference to FIG. 10). For example, in response to acondition of the turbocharger compressor, including one or more ofcondensate formation at the compressor, a compressor inlet temperatureless than a lower threshold temperature, a compressor outlet temperaturegreater than an upper threshold temperature, and a compressor speedgreater than a threshold speed, there may be a request to decrease EGRflow to the intake passage, upstream of the compressor. If there is arequest to decrease EGR (e.g., decrease the amount of exhaust gas flowfrom the engine cylinders to the intake passage via the scavenge exhaustvalves (SVs) and the scavenge manifold), the method proceeds to 1214 toadjust one or more engine actuators to decrease EGR flow from thescavenge manifold to the intake passage. Decreasing EGR at 1214 mayinclude one or more of closing (or decreasing the amount of opening of)the BTCC valve at 1216, retarding the timing (e.g., opening and closingtiming) of the SVs at 1218, and opening (or increasing the amount ofopening of) the SMBV at 1220. The method at 1214 may include selectingwhich one or more of the adjustments at 1216, 1218, and 1220 to utilizeto decrease EGR to the desired level based on engine operatingconditions, as described further below with reference to FIG. 13.

If there is not a request to decrease EGR, the method continues to 1222to determine whether there is a request to increase blowthrough (BT). Asexplained above, increasing blowthrough may include increasing an amountof fresh, non-combusted air (or mixed intake air from the intakemanifold where at least some of the mixed intake air has not undergonecombustion) flowing from an intake valve to a SV during a valve overlapperiod of the intake valve and SV and then flowing to the intake passagevia the scavenge manifold and EGR passage. In one example, there may bea request to increase blowthrough in response to an outlet temperatureof the compressor being above a threshold outlet temperature, engineknock, and/or compressor surge. If there is a request to increaseblowthrough, the method continues to 1224 to increase blowthrough viaone or more of retarding the timing of the SVs at 1226, advancing thetiming of the intake valves (IV) at 1228, and closing the SMBV and/oropening the BTCC valve at 1230. For example, increasing the amount ofopening overlap between the SV and IV of the same cylinder (e.g.,increasing the amount of time both the SV and IV of a same cylinder areopen at the same time) may result in increasing the amount ofblowthrough to the intake. Specifically, increasing the amount ofopening overlap between the IV and SV may include retarding the SVtiming (e.g., retarding the closing timing of the SV) and/or advancingthe IV timing (e.g., advancing the opening timing of the IV). In oneexample, increasing the amount of opening (or fully opening) the BTCCvalve and/or decreasing the amount of opening (or fully closing) theSMBV may increase the amount of blowthrough air flowing from the enginecylinders to the intake passage. However, if the BTCC valve is alreadyfully opened and the SMBV is already fully closed, the method at 1224may include retarding the SV timing and/or advancing the IV timing.Further, if the SV timing is already at the maximum amount of retard,the method at 1224 may include advancing the IV timing to increaseblowthrough to the intake Similarly, if the intake valve timing isalready fully advanced, the method at 1224 may include retarding the SVtiming to increase blowthrough. Further still, the method at 1224 mayinclude first retarding the SV timing and then advancing the IV timingif blowthrough is still not at the requested level when the SV timingreaches the maximum amount of retard. In yet another example, thedecision to adjust more than one of the engine actuators at 1224 may bebased on the amount of requested change in the amount of blowthrough.For example, as the requested blowthrough increases further above thecurrent level, the method at 1224 may include increasing the amount ofadjusting the SV timing, IV timing, and valve positions and/or adjustingat least two or more actuators at 1224 (e.g., at the same time,retarding the SV timing and advancing the IV timing to achieve thedesired blowthrough amount). In this way, increasing blowthrough at 1224may include adjusting one or more of the SV timing, IV timing, SMBV, andBTCC valve based on the current timings and positions of one another andthe magnitude of the requested increase in blowthrough.

If there is not a request to increase blowthrough, the method proceedsto 1232 to determine whether there is a request to decrease blowthrough.In one example, there may be a request to decrease blowthrough inresponse to the turbine operating below a threshold speed and above athreshold load and/or a flow rate through the compressor being above athreshold flow rate (where the threshold flow rate may be a flow rate atwhich compressor efficiency decreases and results in heating of thecharge air). If there is a request to decrease blowthrough, the methodcontinues to 1234 to decrease blowthrough via one or more of advancingSV timing at 1236, retarding IV timing at 1238, and opening the SMBVand/or closing the BTCC valve at 1240. For example, decreasing theamount of opening overlap between the SV and IV of the same cylinder(e.g., decreasing the amount of time both the SV and IV of a samecylinder are open at the same time) may result in decreasing the amountof blowthrough to the intake. Specifically, decreasing the amount ofopening overlap between the IV and SV may include advancing the SVtiming (e.g., advancing the closing timing of the SV) and/or retardingthe IV timing (e.g., retarding the opening timing of the IV). In oneexample, decreasing the amount of opening (or fully closing) the BTCCvalve and/or increasing the amount of opening (or fully opening) theSMBV may decrease the amount of blowthrough air flowing from the enginecylinders to the intake passage. However, if the BTCC valve must remainopen to deliver the requested EGR amount to the intake passage, themethod at 1234 may include advancing the SV timing and/or retarding theIV timing. Further, if the SV timing is already at the maximum amount ofadvance, the method at 1234 may include retarding the IV timing todecrease blowthrough to the intake Similarly, if the intake valve timingis already fully retarded, the method at 1234 may include advancing theSV timing to decrease blowthrough. Further still, the method at 1234 mayinclude first advancing the SV timing and then retarding the IV timingif blowthrough is still not at the requested level when the SV timingreaches the maximum amount of advance. In yet another example, thedecision to adjust more than one of the engine actuators at 1234 may bebased on the amount of requested change in the amount of blowthrough.For example, as the requested blowthrough decreases further below thecurrent level, the method at 1234 may include increasing the amount ofadjusting the SV timing and IV timing, or adjusting both, at the sametime, the SV timing and IV timing to achieve the desired blowthroughamount.

If there is not a request to decrease blowthrough, the method continuesto 1242 to maintain the current valve positions and timings. Method 1200then ends.

FIG. 13 shows a method 1300 for selecting between operating modes toadjust the flow of exhaust gases (e.g., EGR flow) from engine cylindersto the intake passage via scavenge exhaust valves and the scavengeexhaust manifold. Method 1300 may continue from 1204 and 1214 of method1200, as described above. Method 1300 begins at 1302 by determiningwhether first mode conditions are met. In one embodiment, first modeconditions for adjusting EGR flow may include when a requested change inthe EGR flow to the intake is greater than a threshold level. Thethreshold level may be a non-zero, threshold amount of EGR flow that maynot be achievable via only a single actuator adjustment. In anotherembodiment, first mode conditions for adjusting EGR flow to the intakemay include when none of the BTCC valve and SVs are diagnosed as beingmispositioned or degraded (e.g., such as during method 1100, asdescribed above with reference to FIG. 11). If the first mode conditionsare met at 1302, the method continues to 1304 to adjust both the BTCCvalve and the SV timing to adjust the amount of EGR flow to the intakepassage. For example, the method at 1304 may include adjusting together,at a same time, the position of the BTCC valve and the timing of the SVsto adjust the EGR flow to the desired level (e.g., to increase ordecrease EGR flow, as described above with reference to FIG. 12). Inanother example, the method at 1304 may include first adjusting one ofthe BTCC valve position and the SV timing and then, directly followingadjusting the first actuator, adjusting the other one of the BTCC valveposition and the SV timing. In this way, adjusting the BTCC valve (e.g.,opening) may adjust (e.g., increase or decrease) the EGR flow by a firstamount and adjusting the SV timing (e.g., advancing or retarding) mayadjust the EGR flow by a second amount. Thus, a larger adjustment in EGRflow may be achieved by adjusting both the BTCC valve position and theSV timing during the first mode.

Alternatively at 1302, if the first mode conditions are not met, themethod continues to 1306 to determine whether the second mode conditionsfor adjusting EGR flow are met. In one embodiment, the second modeconditions may include one or more of when the timing of the SVs cannotbe adjusted further for a current demanded direction of adjustment ofthe EGR flow and when the BTCC valve is in a partially open position andthere is a request for both increased EGR flow and increased blowthroughair from the SVs to the intake passage. For example, the SV timing maynot be able to be further adjusted if it is already at its maximumamount of retard (in the case of decreasing EGR flow) or advance (in thecase of increasing EGR flow). In another embodiment, the second modeconditions may additionally or alternatively include when the differencebetween an actual timing of the SVs and an expected timing of the SVs isgreater than a threshold (e.g., as explained above with reference tomethod 1100 of FIG. 11). Thus, if the SVs are diagnosed as not being atthe correct timing or being degraded, they may not be used to adjust EGRflow. In this case, the BTCC valve may be adjusted to adjust the EGRflow to the desired level based on the actual timing of the SVs. If thesecond mode conditions are met at 1306, the method proceeds to 1308 toadjust only the BTCC valve to adjust the EGR flow to the desired level.For example, the method at 1308 may include only adjusting the positionof the BTCC valve (e.g., increasing or decreasing the amount of openingor modulating the position between fully opened and fully closed) toadjust the EGR flow to the desired level and not adjusting the SVtiming.

Alternatively at 1306, if the second mode conditions are not met, themethod continues to 1310 to determine whether the third mode conditionsfor adjusting EGR flow are met. In one embodiment, the third modeconditions may include when the BTCC valve is already in a fully openposition and in response to a request to increase the flow of exhaustgas from the SVs to the intake passage. In another embodiment, the thirdmode conditions may additionally or alternatively include when thedifference between the actual pressure drop across the BTCC valve andthe expected pressure drop across the BTCC valve is greater than athreshold (e.g., as explained above with reference to method 1100 ofFIG. 11). Thus, if the BTCC valve is diagnosed as mispositioned ordegraded, it may not be used to adjust EGR flow. If the third modeconditions are met at 1310, the method proceeds to 1312 to adjust onlythe SV timing to adjust EGR flow. For example, the method t 1312 mayinclude advancing or retarding the SV timing to adjust the EGR flow tothe desired level and not adjusting the BTCC valve. As one example, ifthe BTCC valve is already fully opened and there is a request toincrease EGR flow, the method at 1312 includes maintaining the BTCCvalve in a fully open position and adjusting the timing of the SVs toadjust the EGR flow to the desired level.

If the third mode conditions are not met at 1310, the method continuesto 1314 to maintain the SV timing and BTCC valve position at the currenttimings/positions. Method 1300 then ends.

FIG. 22 shows a graph 2200 of controlling one or more engine actuatorsto adjust EGR flow and blowthrough flow to the intake passage from thescavenge exhaust valves. Specifically, graph 2200 depicts changes in EGRflow at plot 2202, changes in blowthrough flow (BT) at plot 2204,changes in a position of the BTCC valve at plot 2206, changes in SVtiming at plot 2208 (relative to a default timing, D1, for best fueleconomy, a maximum amount of advance, MA, and a maximum amount ofretard, MR), changes in a position of the SMBV at plot 2210, changes inIV timing at plot 2212 (relative to a default timing, D2, for best fueleconomy, a maximum amount of advance, MA, and a maximum amount ofretard, MR), changes in a difference between an actual pressure drop andexpected pressure drop across the BTCC valve (e.g., during valvediagnosis) at plot 2214, and changes in a difference between an actualtiming and expected timing of the SVs at plot 2216.

Prior to time t1, the BTCC valve is fully opened, the SMBV is fullyclosed, IV timing is at its default timing D2, and SV timing is at itsdefault timing D1. At time t1, there may be a request to increase EGRflow to the intake passage to a first level. In response to this requestand because the BTCC valve is already in the fully open position, the SVtiming is advanced to increase the EGR flow to the first level.Advancing the SV timing may also decrease BT. Thus, at time t2 there isa request to increase BT. However, since the EGR flow demand may stillbe at the first level, the intake valve timing is advanced at t2 whilethe SV timing is maintained at the advanced timing.

Prior to time t3, the difference between the actual and expected timingof the SVs increases above a threshold T2. Then, at time t3, there maybe a request to decrease EGR flow and blowthrough. Thus, in response tothe request and the diagnosis of the SV timing, at time t3, the BTCCvalve is closed to decrease EGR flow and BT. Further, since the BTCCvalve is closed, the intake valve timing may be returned to the defaulttiming D2. Between time t3 and time t4, the position of the BTCC valvemay be modulated between fully opened and fully closed to achieve thedesired EGR flow to the intake. In alternate embodiments where the BTCCvalve is a continuously variable valve adjustable into a plurality ofpositions between and including fully open and fully closed, the BTCCvalve may be adjusted into and maintained at a partially closed positionthat delivers the desired EGR flow to the intake (e.g., instead of beingmodulated). Prior to time t4, the difference between the actual andexpected SV timing may reduce back below the threshold T2. At time t4,there may again be a request to increase EGR, but to a second level thatis higher than the first level requested at time t1. In response to thishigher request that may be above a threshold increase in EGR flow, theBTCC valve is opened at time t4 and the SV timing is advanced. The IVtiming may also be advanced at time t4 to maintain the BT at the desiredlevel. In this way, both the BTCC valve and the SV timing areconcurrently adjusted to adjust the EGR flow to the requested secondlevel.

At time t5 there may be a request to decrease EGR flow. However, justbefore time t5, the difference between the actual and expected pressuredrop across the BTCC valve may increase of a threshold T1. In responseto the request and the diagnosis of the BTCC valve, the SV timing isretarded. However, at time t6 the SV timing may reach its maximum amountof retard but the EGR flow may still need to be reduced further. As aresult, the SMBV may be opened to further reduce EGR flow to the intakepassage. In this way, under different operating modes, one or moreactuators (e.g., the BTCC valve, SV timing, IV timing, and/or the SMBV)may be adjusted to achieve the desired EGR flow and BT flow. Forexample, during a first mode, as shown at time t4, both the SV timingand BTCC valve are adjusted to deliver the desired EGR flow to theintake passage. As another example, during a second mode, as shown attime t3, only the BTCC valve is adjusted to deliver the desired EGR flowsince the SVs are diagnosed as not being at the correct timing (and maypossible have degraded function). However, at this time, the IV timingis also adjusted to maintain the desired BT flow. Further, during athird mode, as shown at time t5, only the SV timing is adjusted toadjust the EGR flow since the BTCC valve is diagnosed as having degradedfunction and/or being mispositioned. However, at time t6, when the SVtiming reaches its maximum amount of retard, the SMBV is opened, inaddition to the retarding SV timing, to achieve the higher desired EGRlevel. Adjusting the different valve actuators in coordination with oneanother (e.g., based on one another's current position, timing, and/ordegradation or mispositioning state) may enable efficient delivery ofboth a desired EGR flow and BT flow amount to the intake passage via theSVs. A technical effect of adjusting a flow of exhaust gas from thescavenge exhaust valves to the intake passage, upstream of thecompressor, via adjusting one or both of the BTCC valve and the timingof the scavenge exhaust valves, in the different modes described above,is delivering the desired EGR flow and blowthrough flow to the intake,even when one of the BTCC valve or SV timing is not able to be adjusted.Further, controlling the EGR flow in the third mode by adjusting onlythe SV timing may provide a more consistent EGR flow where a fixedamount of EGR is pushed to the intake passage in each engine cycle. Forexample, controlling the EGR flow in this way may allow the EGR valve tobe an on/off valve, thereby simplifying EGR valve control and reducingengine system costs.

FIG. 14 shows a method 1400 for operating the vehicle in the electricmode (e.g., electric-only mode). Method 1400 may continue from 405 ofmethod 400, as described above. Method 1400 begins at 1402 by propellingthe hybrid electric vehicle via motor torque only. For example, one ormore clutches may be moved to disconnect the crankshaft of the enginefrom an electric machine and the components connected thereto andconnect the electric machine with the transmission and wheels of thevehicle (such as the electric machine 161, transmission 167, andclutches 166 shown in FIG. 1B). In this way, the electric machine (e.g.,motor) may provide torque to the vehicle wheels (using electrical powerreceived from a traction battery).

At 1404, the method includes determining whether an engine start isimminent As one example, the controller may determine than an enginestart (e.g., where the engine must be started to begin combusting toprovide torque to propel the vehicle) is imminent in response to thebattery state of charge and the driver torque demand. For example, ifthe demanded torque cannot be provided by the battery (at the currentstate of charge), a request to start the engine and operate the vehiclein the engine mode may be generated. In another example, if the demandedtorque can only be provided by the battery for a limited duration, arequest to start the engine within that limited duration may begenerated. This duration may be based on an amount of time to increasethe intake manifold pressure and/or piston temperature above thresholdlevels for starting the engine with reduced emissions, as describedfurther below. However, if the demanded torque can be provided by onlythe battery (e.g., for longer than the limited duration), and thus anengine start is not imminent, the method may continue to 1406 todetermine whether the vehicle is decelerating. In one example, thevehicle may be decelerating if an accelerator pedal is released and/or abrake pedal is depressed. In another example, the vehicle may bedecelerating if engine speed is decreasing. If the vehicle is notdecelerating, the method continues to 1407 to continue propel thevehicle via motor torque only. However, if the controller determinesthat the vehicle is decelerating, the method continues to 1408 todeactivate all blowdown exhaust valves (e.g., first exhaust valves 8shown in FIG. 1A) of the engine cylinders and rotate the engine (via thecrankshaft) using torque from the vehicle wheels instead of charging thebattery. In one example, deactivating all the blowdown exhaust valvesmay include the controller deactivating one or more valve actuationsystems of the blowdown exhaust valves to maintain the blowdown exhaustvalves closed so that no gases travel to the exhaust passage via thecylinders. As a result, no gases may travel through the exhaust passage,thereby decreasing engine emissions. Rotating (e.g., spinning) theengine during the deceleration may result in warming up the engine,thereby increasing engine performance and reducing engine emissions uponengine startup.

Returning to 1404, if an engine start is imminent, the method continuesto 1410 to determine whether to operate in a blowdown valve deactivationmode prior to the engine start (e.g., prior to the engine firing). Inone embodiment, the controller may determine to operate the engine inthe blowdown deactivation mode in response to an intake manifoldpressure being above a threshold pressure. The threshold pressure may bebased on an intake manifold pressure at which increased emissions mayoccur upon engine startup. In one example, the threshold pressure may bea pressure at or above atmospheric pressure. In another embodiment, thecontroller may determine not to operate the engine in the blowdowndeactivation mode and to instead operate in an extended crank mode inresponse to a piston temperature being less than a thresholdtemperature. The threshold temperature may be a threshold temperaturefor restarting the engine with reduced emissions. For example, if theengine starts with the piston temperature below the thresholdtemperature, increased emissions may result. In one example, whether tooperate in the blowdown valve deactivation mode or the extended crankmode, may be determined based on a threshold cylinder (or piston)temperature at which fuel is evaporated. Thus, the decision at 1410 mayalso be based on fuel type. If the piston (or cylinder) temperature isbelow the threshold temperature, which may be the temperature necessaryto evaporate the current fuel type, the controller may determine tooperate the engine in the extended crank mode at 1410

If the blowdown valve deactivation mode is chosen at 1410, the methodcontinues to 1412 to deactivate all the blowdown exhaust valves (e.g.,deactivate the blowdown exhaust valve 8 of each cylinder, as shown inFIG. 1A) prior to engine cranking As a result, no gases passing throughthe engine cylinders may flow to the exhaust passage. At 1414, themethod includes circulating gases through the engine cylinders and backto the turbocharger compressor inlet (e.g., compressor 162 shown in FIG.1A) via the scavenge exhaust manifold (e.g., second exhaust manifold 80shown in FIG. 1A) and the scavenge exhaust valves (e.g., scavengeexhaust valves 6 shown in FIG. 1A) to pump the intake manifold pressuredown. In this way, gases may enter the engine cylinders via the intakemanifold, exit the engine cylinders via the scavenge exhaust valve ofeach cylinder, and then flow into the scavenge exhaust manifold, throughthe EGR passage, to the intake passage, and back to the intake manifold.This may be repeated for multiple rotations of the crankshaft Forexample, the method at 1414 may be repeated until the manifold pressuredecreases below a lower threshold pressure or until an indication thatthe engine needs to be started is received. At 1416, if it is decidedthat it is time to start the engine (e.g., based on the intake manifoldpressure decreasing below the lower threshold pressure for the enginestart and/or based on the torque demand no longer being able to besupplied by the battery), the method continues to 1418 to determinewhether a catalyst disposed in the exhaust passage (e.g., emissioncontrol device 70 and/or 72 shown in FIG. 1A) is at a light-offtemperature. If the catalyst is not at the light-off temperature, themethod continues to 1420 to reactivate the blowdown exhaust valves ofthe inside cylinders while maintaining the blowdown exhaust valves ofthe outside cylinder deactivated and firing the cylinders. As oneexample, the inside cylinders may include the cylinder oriented insideof and between the outside cylinders of the engine (e.g., as shown inFIG. 1A, cylinders 14 and 16 are inside cylinders and cylinders 12 and18 are outside cylinders). This may help the catalyst(s) to reach theirlight-off temperatures more quickly. Alternately at 1418, if thecatalyst is at the light-off temperature, the method continues to 1422to reactivate all the blowdown exhaust valves of all the cylinders,inject fuel into each of the cylinders, and resume combustion at each ofthe cylinders. As a result, the vehicle may begin operating in theengine (e.g., engine-only or assist mode) mode and stop operating in theelectric-only mode.

Returning to 1410, if it is determined that the engine should operate inthe extended crank mode instead of the blowdown valve deactivation mode,the method continues from 1410 to 1424. At 1424, the method includesoperating in the extended crank mode by rotating the engine unfueled viathe motor (e.g., electric motor) slowly. The method at 1424 furtherincludes heating each cylinder during a compressor stroke of thecylinder. For example, the method at 1424 may include, while propellingthe hybrid vehicle via only motor torque and before engine restart,rotating the engine unfueled via the motor torque at lower than athreshold speed. Herein, the electric motor of the vehicle may bepropelling the vehicle and rotating the engine. The threshold speed maybe, in one example, an engine cranking speed. That is, the engine may bespun at a speed slower than the speed at which the engine would havebeen spun by a starter motor during engine crank and restart. Forexample, during engine cranking, the engine may be rotated unfueled viaa starter motor at 150 rpm. In comparison, during the slow rotating forcylinder heating, the engine may be rotated at 10-30 rpm via theelectric motor/generator of the hybrid vehicle. In alternate examples,the threshold speed at or below which the engine is slowly rotated maybe higher or lower based on operating parameters such as oiltemperature, ambient temperature, or NVH. In one example, slow enginerotating may be initiated in a cylinder (e.g., a first cylinder)selected based on a proximity of a cylinder piston position relative toa compression stroke TDC. For example, a controller may identify acylinder having a piston positioned closest to compression stroke TDC orat a position where at least a threshold level of compression isexperienced. The engine is then rotated so that each cylinder issequentially heated during a compression stroke of the cylinder. Asrotation continues, each cylinder may be cooled during an expansionstroke of the cylinder, immediately following the compression stroke.However, the cylinder may be heated more during the compression strokethan the cylinder is cooled during the expansion stroke allowing for anet heating of each cylinder via a heat pump effect. As such, during acompression stroke of each cylinder, aircharge is compressed, generatingheat. By rotating an engine so that a cylinder is held in thecompression stroke, heat from the compressed air can be transferred tothe cylinder walls, cylinder head, and piston, raising enginetemperature.

Continuing to 1426, the method includes throttling the BTCC valve (e.g.,first EGR valve 54 shown in FIG. 1A) or the hot pipe valve (e.g., thirdvalve 32 shown in FIG. 1A) to increase the cranking torque and, as aresult, further heat the engine. In one example, throttling the BTCCvalve or the hot pipe valve may include at least partially closing (ordecreasing the amount of opening of) the BTCC valve or the hot pipevalve. In some examples at 1426, the intake throttle and the BTCC valvemay be closed to recirculate gases through the cylinders via the hotpipe (and not the EGR passage) while the hot pipe valve is partiallyclosed (e.g., throttled) to increase cranking torque. In other example,the intake throttle may remain open and the hot pipe valve may be fullyclosed to recirculate gases through the cylinders via the EGR passage(e.g., first EGR passage 50 shown in FIG. 1A) while the BTCC valve ispartially closed (e.g., throttled) to increase cranking torque. At 1428,the method includes determining whether it is time to start (e.g.,restart) the engine. In one example, the engine may not be started untilthe piston temperature increases above the threshold temperature. If itis not time to start the engine, the method returns to 1424 and 1426 tocontinue operating in the extended crank mode. Otherwise, if it is timeto start the engine, the method continues to 1422 to restart the engine,as described above.

FIG. 23 shows a graph 2300 of operating the hybrid electric vehicle inthe electric mode to heat the engine system prior to starting theengine. Specifically, graph 2300 depicts vehicle speed at plot 2302,battery state of charge (SOC) at plot 2304, intake manifold pressure(MAP) at plot 2306, piston temperature at plot 2308, catalysttemperature at plot 2310, engine speed at plot 2312, an activation stateof cylinder blowdown exhaust valve (BDVs) at plot 2314, a position ofthe BTCC valve (e.g., first EGR valve 54 shown in FIG. 1A) at plot 2316,a position of a hot pipe valve (e.g., valve 32 shown in FIG. 1A) at plot2318, and a position of an intake throttle (e.g., throttle 62 shown inFIG. 1A) at plot 2320. All plots are shown over time along the x-axis.

The vehicle may be operating in an electric mode and propelled via motortorque only prior to time t1. For example, engine start conditions maynot be met prior to time t1. Between time t1 and t2, as operator torquedemand and correspondingly vehicle speed vary, the battery SOC may varywith the battery SOC being reduced at a higher rate when the vehiclespeed increases. While the vehicle is propelled using motor torquebetween time t1 and t2, the piston temperature may be below thresholdtemperature T1 and MAP may be above threshold pressure P1.

At time t2, operator torque demand and vehicle speed decrease. As aresult, the battery SOC may stop decreasing, or decrease at a slowlyrate. Shortly after time t2, a vehicle deceleration event occurs. Duringthis event, instead of dissipating the wheel torque as heat or using itto recharge the battery, the engine is opportunistically rotated,unfueled, via the wheels and the blowdown exhaust valves of all theengine cylinders are deactivated. For example, at least some of thewheel torque is applied to engine rotation via a motor/generator of thevehicle with a transient increase in the speed of engine rotation. As aresult of rotating the engine and deactivating the blowdown valves, airis recirculated through the engine via the scavenge exhaust valves, EGRpassage, and open BTCC valve and thus, the piston temperature isincreased. Once the vehicle speed drops, the opportunistic enginerotation is stopped. In alternate embodiments, in an engine systemincluding a hot pipe (e.g., hot pipe 30 shown in FIG. 1A) coupledbetween the scavenge exhaust manifold and the intake manifold,downstream of an intake throttle, the intake throttle and BTCC valve maybe closed while a valve in the hot pipe is opened to allow recirculationof air through the engine cylinders via the scavenge exhaust valves andthe hot pipe.

At time t3, the deceleration event ends and the vehicle speed increasesagain. At time t4, there may be an indication that an engine start isimminent In response to the MAP being above the threshold pressure P1and piston temperature being above the threshold temperature T1 duringthe indication of the imminent engine start, all the BDVs of all theengine cylinders are again deactivated. While the BTCC valve is open,gases are circulated through the engine cylinders and back to the intakepassage via the scavenge exhaust valves, the scavenge exhaust manifold,and the EGR passage. As a result, the intake manifold pressuredecreases. At time t5, the intake manifold pressure decreases below thethreshold pressure P1. As a result, the engine may be started. However,since the catalyst temperature is below the light-off temperature T2,the BDVs of only the inside engine cylinders may be reactivated whilethe BDVs of the outside cylinders remain deactivated. Then, when thecatalyst temperature increases above the light-off temperature T2 attime t6, the BDVs of the outside cylinders are reactivated.

After a duration of time (e.g., after an engine shutdown and/or key-offshutdown of the vehicle), the vehicle may again be operating in theelectric mode and propelled entirely via motor torque. At time t7, theremay be an indication that an engine start is imminent while pistontemperature is below the threshold temperature T1. In response, thevehicle may be operated in an extended crank mode where the engine isrotated unfueled via the electric motor slowly (e.g., at less than acranking speed). While rotating the engine, the BTCC valve may beclosed, the hot pipe valve at least partially opened, and the intakethrottle closed. Further, the hot pipe valve may not be fully opened (sothat it is partially throttled) in order to increase cranking torque andfurther increase heating of the engine. As a result of this operation,air is warmed in the cylinders during the compression stroke and thenrecirculated through the engine system via the scavenge exhaust valves,scavenge exhaust manifold, hot pipe, and intake manifold, therebyincreasing piston temperature. At time t8, the piston temperatureincreases above the threshold temperature T1. As a result, the engine isrestarted and the BTCC valve and intake throttle are opened and the hotpipe valve is closed.

In this way, an engine of a hybrid vehicle may be slowly cranked using amotor during a transition from operating in an electric mode to anengine mode to heat the engine before an engine start. By slowlyspinning the engine, unfueled, for a duration before an engine restart,heat generated from air compressed in a cylinder during a compressionstroke can be transferred to cylinder walls and pistons, andadvantageously used to heat the engine. Further, by throttling the hotpipe valve (or BTCC valve if gases are recirculated via the EGR passageinstead of the hot pipe), the cranking torque is increased, therebyfurther increasing the warming of the engine. Thus, a technical effectof rotating the engine unfueled via motor torque at less than a crankingspeed while at least partially throttling the BTCC valve or hot pipevalve, is increasing the piston temperature and the rest of the engine,thereby reducing cold start emissions and starting the engine morequickly. In another example, by deactivating the blowdown exhaust valvesand recirculating air through the engine cylinders, scavenge exhaustmanifold, and EGR passage, the intake manifold pressure may be pumpeddown and/or the engine temperature may be increased. In this way, theengine may be started more quickly and overall engine cold-start exhaustemissions and engine performance can be improved. Thus, a technicaleffect of deactivating the blowdown exhaust valves and circulating airthrough the engine cylinders during the electric mode is decreasing theintake manifold pressure, increasing the engine temperature, and thus,starting the engine more quickly while reducing emissions.

FIG. 15 shows a method for operating the engine system in a shutdownmode. Method 1500 may continue from 426 of method 400, as describedabove. Method 1500 begins at 1502 by determining if the detected orindicated shutdown event is a key off shutdown. In one example, theindicated shutdown event may be determined to be a key off shutdownevent in response to the controller receiving a signal that an ignition(operated by a user) of the engine has been turned off. In anotherexample, the indicated shutdown event may be determined to be a key offshutdown event in response to the controller receiving signal that theengine has been turned off (e.g., via an ignition being turned off) andthe vehicle being put in park. In this way, the key off shutdown may bea shutdown during which the engine is expected to be turned off for athreshold amount of time and not restarted for a duration. If theshutdown at 1502 is a key off shutdown, the method continues to 1504 toclose the intake throttle (e.g., throttle 62 shown in FIG. 1A) and openthe hot pipe valve (e.g., valve 32 shown in FIG. 1A) to pump unburnedhydrocarbons to a catalyst (e.g., one of emission control devices 70 and72 shown in FIG. 1A) in the exhaust passage of the engine. During thistime, the blowdown exhaust valves may remain activated. Further, themethod at 1504 may further include, during the closing the intakethrottle and opening the first hot pipe valve, closing the BTCC valve(e.g., valve 54 shown in FIG. 1A). As a result, unburned hydrocarbonsmay be recirculated from engine cylinders back to the intake manifoldvia the scavenge exhaust valves, scavenge exhaust manifold, and hot pipe(e.g., passage 30 shown in FIG. 1A). The recirculated unburnedhydrocarbons may then be pumped from the engine cylinders to the exhaustpassage including the catalyst via the blowdown exhaust valves. This mayreduce the amount of hydrocarbons in the engine while the engine is shutdown and may maintain the catalyst at stoichiometry at shutdown and fora subsequent restart.

At 1506, the method includes, as the engine stops rotating, opening theBTCC valve and then opening the throttle. For example, in response to acrankshaft of the engine stopping rotating, the controller may actuatean actuator of the BTCC valve to open the BTCC valve and an actuator ofthe throttle to open the throttle. This may reduce the amount of exhaustgases pulled back into the intake (e.g., intake passage) of the engine.Further, the method at 1506 may include first opening the BTCC valve andthen, in response to the BTCC valve being opened, opening the throttle.

Returning to 1502, if the shutdown is not a key off shutdown, the methodmay determine the shutdown to be a start/stop shutdown and thus continueto 1508. As one example, the controller may determine that the shutdownis a start/stop shutdown request responsive to the vehicle being stoppedfor a threshold duration but not keyed off (e.g., when the vehicle isstopped at a stoplight). At 1508 the method includes initiating thestart/stop shutdown. The method then continues to 1510 to disable (e.g.,deactivate) all the blowdown exhaust valves (e.g., valves 8 shown inFIG. 1A) of the engine and open the BTCC valve, after the last cylinderof all the engine cylinders has been fired. Said another way, once thefinal cylinder fires (e.g., the final cylinder that undergoes combustionbefore no more cylinders are fired and the engine shuts down), thecontroller may deactivate the valve actuators of the blowdown exhaustvalves such that the blowdown exhaust valves remain closed and do notexhaust gases to the exhaust passage. As a result, gases from all theengine cylinders are recirculated to the intake manifold via thescavenge exhaust valves and the EGR passage. This will run down thepressure in the intake manifold during engine rundown (e.g., while thespeed of the crankshaft decreases and eventually comes to a stop).

At 1512, the method includes determining if there is a request torestart the engine. In one example, the request to restart the enginemay be generated in response to an increase in torque demand from astopped position of the vehicle. For example, if a brake pedal isreleased and/or an accelerator pedal of the vehicle is depressed, arestart request may be generated. If there is not a request to restartthe engine, the method continues to 1516 to maintain the blowdownexhaust valves disabled and the BTCC valve in the open position.Otherwise, if there is a request to restart the engine, the methodcontinues to 1514 to reactivate the blowdown exhaust valves upon aninitial cranking operation of the crankshaft Regular engine operation isthen resumed. For example, the method may end and/or return to method400. As explained above, reactivating the blowdown exhaust valves mayinclude the controller sending a signal to the valve actuators of theblowdown exhaust valves to resume opening and closing the blowdownexhaust valves at their set timing.

FIG. 24 shows a graph 2400 of operating the split exhaust engine systemof the vehicle in the shutdown mode. Specifically, graph 2400 depictswhether an ignition of the vehicle is on or off at plot 2402, vehiclespeed at plot 2404, a position of the throttle at plot 2406, a positionof the BTCC valve at plot 2408, a position of the hot pipe valve at plot2410, engine speed at plot 2412, and an activation state (e.g., on/offor enabled/disabled) of the blowdown exhaust valves (BDVs) at plot 2414.All plots are shown over time along the x-axis.

Prior to time t1, the engine is operating and vehicle speed is above astationary level (e.g., a level at which the vehicle may be stationaryand not moving). Further, all BDVs of all engine cylinders are activatedand operating at their set timing (which is different than the openingtiming of the scavenge exhaust valves) prior to time t1. At time t1, thevehicle speed decreases to approximately zero, thereby indicating thatthe vehicle is stopped. The ignition of the engine remains on at timet1. In response to the vehicle being stopped, a start/stop shutdown isinitiated. This may include firing a last engine cylinder at time t2.Then, in response to firing the last engine cylinder, all the BDVs(e.g., each BDV of each cylinder) are disabled at time t2 at the BTCCvalve is opened. During this time, the scavenge exhaust valves mayremain active and thus gases from the engine cylinders are routed to theintake passage via the scavenge exhaust manifold and EGR passage. Whenthe BDVs are disabled, they may remain closed and thus no gases from theengine cylinders are routed to the exhaust passage of the engine. Justbefore time t3, a request to restart the engine may be received by thecontroller (e.g., via an operator releasing a brake pedal and pressingan accelerator pedal, thereby indicating an increase in torque demandfrom the stopped position). The crankshaft is cranked at time t3 andthus the engine speed begins to increase. At the initial crank at timet3, the BDVs are reactivated. The cylinders begin firing again and atleast some exhaust gases may be directed to the exhaust passage via theBDVs. Regular engine operation is resumed.

After a period of time, at time t4, the vehicle speed decreases tosubstantially zero, indicating that the vehicle has stopped. At time t5,the ignition to the engine is turned off (e.g., manually turned off viaa vehicle operator). In response to the vehicle be stopped (e.g., inpark) and the engine being turned off via the ignition (e.g., keyedoff), the throttle is closed, the BTCC valve is close, and the hot pipevalve is opened. As a result, engine gases are recirculated via thescavenge exhaust manifold and the hot pipe, thereby decreasing intakemanifold pressure. As the engine stops rotating (engine speed reachesapproximately zero), the throttle and the BTCC valve are both opened.

In this way, during a key off engine shutdown (as shown at time t5) or astart/stop shutdown (as shown at time t1), the throttle valve, BTCCvalve, BDVs, and/or hot pipe valve may be adjusted to reduce the amountof hydrocarbons in the intake of the engine, reduce the intake manifoldpressure, and bring a catalyst to or near stoichiometry. This may reduceengine emissions during the shutdown and improve engine operation (andreduce emissions) during a subsequent engine start or restart. Atechnical effect of closing the intake throttle and opening the hot pipevalve in response to a request to shut down the engine (e.g., key offrequest) is reducing engine reversal and flowing unburned hydrocarbonsto the catalyst in the exhaust, thereby reducing hydrocarbons in theengine system and maintaining the catalyst at stoichiometry. A technicaleffect of deactivating the BDVs and opening the BTCC valve isrecirculating gases through the engine, thereby reducing the intakemanifold pressure before shutting down the engine.

FIG. 25 shows a graph 2500 of example operation of the split exhaustengine from startup to shutdown. Specifically, graph 2500 depicts anactivation state of the scavenge exhaust valves (SV, where on isactivated and off is deactivated) at plot 2502, a position of the BTCCvalve at plot 2504, EGR flow (e.g., through the EGR passage 50 and tothe compressor inlet, as shown in FIG. 1A) at plot 2506, a temperatureof an exhaust catalyst (e.g., such as a catalyst of one of emissioncontrol devices 70 and 72 shown in FIG. 1A) relative to a light-offtemperature T1 at plot 2508, a temperature at an outlet of theturbocharger compressor (e.g., compressor 162 shown in FIG. 1A) relativeto a threshold outlet temperature T2 at plot 2509, a position of anintake throttle (e.g., throttle 62 shown in FIG. 1A) at plot 2510, anactivation state of the blowdown exhaust valves (BDVs) of outsidecylinders (e.g., cylinders 12 and 18 shown in FIG. 1A) at plot 2512, anactivation state of the BDVs of inside cylinders (e.g., cylinders 14 and16 shown in FIG. 1A) at plot 2513, a cam timing of the intake valves atplot 2514 and the exhaust valves (which may include the blowdown exhaustvalves and the scavenge exhaust valves when they are controlled on thesame cam timing system) at plot 2516 relative to their base timings B1(an example of the base cam timings of the intake and exhaust valves maybe shown in FIG. 3B, as described above), a position of the hot pipevalve (e.g., valve 32 shown in FIG. 1A) at plot 2518, a position of theSMBV (e.g., SMBV 97 shown in FIG. 1A), engine speed at plot 2522, andengine load at plot 2524. All plots are shown over time along thex-axis.

Prior to time t1, the engine starts (e.g., in response to an operator ofthe vehicle turning on an ignition) with the scavenge exhaust valvesdefault activated. As such, the scavenge exhaust valves may open andclose at their set timing in the engine cycle. At time t1, the BTCCvalve is opened for the initial crank. As such, the EGR flow begins toincrease after time t1 (and may increase and decrease over time with theopening and closing of the BTCC valve, respectively). After firing thefirst cylinder, the BTCC valve is modulated to control EGR flow to adesired level. Also between time t1 and time t2, the hot pipe valve andSMBV are closed and both the intake and exhaust valve timings are attheir base timings B1. At time t2, the scavenge exhaust valves can beadjusted (e.g., due to the oil pressure having reached a threshold toadjust the valves), so the scavenge exhaust valves are deactivated(e.g., turned off). After time t2, the catalyst temperature is stillbelow its light-off temperature T1. Thus, the BDVs of the outsidecylinders (e.g., cylinders 12 and 18 shown in FIG. 1A) are deactivatedto reduce heat loss during catalyst light off. Further, compression heatmay warm up the cylinder further since airflow to all cylinders ismaintained during the BDV deactivation. This may result in warming ofthe catalyst to a temperature above the light-off temperature T1.

At time t3, the catalyst temperature increases above its light-offtemperature T1 and there may also be a request to increase EGR flow tothe intake passage via the EGR passage and scavenge manifold. Inresponse to the request to increase EGR flow, the BTCC valve ismaintained open and the SV timing is advanced at time t3. Just beforetime t4, engine load decreases below a threshold load L1 and thethrottle position is adjusted to a partially closed position (e.g., partthrottle). In response to this low load condition, at time t4 thethrottle is closed, the BTCC valve is opened, and the hot pipe valve isopened to operate the engine in a hot pipe mode. At time t5, there is anincrease in torque demand (and thus engine load increases). As a result,an electric compressor may be turned on to increase boost pressure. Inresponse to the electric compressor turning on, the BTCC valve may beclosed. At time t6, the electric compressor may be turned off uponreaching the target boost pressure and there may also be a request forincreased EGR. In response to this request (which may be over athreshold amount of EGR flow), both the BTCC valve is opened and the SVtiming is advanced to increase EGR flow. The IV timing may also beadvanced at time t6 to maintain blowthrough to the intake at the desiredlevel while advancing the SV timing to increase EGR flow. Between timet6 and time t7 engine load continues to increase and thus EGR flow tothe intake passage, upstream of the compressor also increases.

At time t7, the outlet temperature of the compressor increases above athreshold outlet temperature T2. In response to this increase, theposition of the BTCC valve is modulated to decrease EGR flow, the SMBVis opened, the SV timing is retarded, and the IV timing is advanced. Asa result, EGR flow to the intake passage, upstream of the compressordecreases and the compressor outlet temperature decreases. At time t8,there is a sudden decrease in engine load that may result from anoperator taking their foot off of an accelerator pedal. Thus, adeceleration fuel shutoff (DFSO) event may occur where fueling isstopped to all cylinders of the engine. As a result of stopping fuelingduring the DFSO event, all the BDVs of all the engine cylinders aredeactivated. In alternate embodiments, only a portion of the BDVs may bedeactivated (e.g., the BDVs of only the inside or outside cylinder, orfor three out of four engine cylinders). In response to the DFSO eventending due to an increase in load at time t9, the BDVs are reactivatedand fuel injection to the engine cylinders is reactivated.

At time t10, the vehicle stops and thus the engine load decreases tozero. At this time, a vehicle operator may put the vehicle in park andturn off the ignition of the engine. As a result, of the key-offshutdown event at time t10, the throttle is closed, the BTCC valve isclosed, and the hot pipe valve is opened. As a result, engine gases arerecirculated via the scavenge exhaust manifold and the hot pipe, therebydecreasing intake manifold pressure. As the engine stops rotating(engine speed reaches approximately zero) at time t11, the throttle andthe BTCC valve are both reopened.

In this way, a split exhaust engine with a scavenge, first exhaustmanifold that routes EGR and blowthrough air to an intake of the engine,upstream of a turbocharger compressor, and a blowdown, second exhaustmanifold that routes exhaust to a turbocharger turbine in an exhaustpassage of the engine (such as the engine shown in FIGS. 1A-1B) may beoperated under different engine operating modes to reduce emissions,increase torque output, reduce knock, and increase engine efficiency.

As one embodiment, a method for an engine includes, in response to arequest to shut down the engine: closing an intake throttle and openinga first valve disposed in a secondary flow passage coupled between anintake manifold, downstream of the intake throttle, and a first exhaustmanifold coupled to a first set of exhaust valves to route unburnedhydrocarbons to a catalyst disposed in an exhaust passage coupled to asecond set of exhaust valves. In a first example of the method, themethod further includes, during the closing the intake throttle andopening the first valve, closing a second valve disposed in an exhaustgas recirculation passage coupled between the first exhaust manifold andan intake passage, upstream of the intake throttle. A second example ofthe method optionally includes the first example and further includes,in response to the engine stopping rotating, opening the second valveand opening the intake throttle. A third example of the methodoptionally includes one or more of the first and second examples, andfurther includes, wherein opening the second valve and opening theintake throttle includes first opening the second valve and then openingthe intake throttle. A fourth example of the method optionally includesone or more of the first through third examples, and further includes,wherein the request to shut down the engine is a key off requestgenerated in response to an operator turning off a vehicle in which theengine is installed. A fifth example of the method optionally includesone or more of the first through fourth examples, and further includesoperating the first set of exhaust valves at a different opening andclosing timing than the second set of exhaust valves. A sixth example ofthe method optionally includes one or more of the first through fifthexamples, and further includes routing the unburned hydrocarbons fromthe first exhaust manifold, through the secondary flow passage, into theintake manifold, through engine cylinders, and to the catalyst via thesecond set of exhaust valves while the intake throttle is closed and thefirst valve is opened. A seventh example of the method optionallyincludes one or more of the first through sixth examples, and furtherincludes, wherein the exhaust passage is coupled to a second exhaustmanifold, the second exhaust manifold coupled to the second set ofexhaust valves.

As another embodiment, a method for an engine includes, in response to arequest to shut down the engine: deactivating all valves of a first setof exhaust valves configured to flow exhaust to an exhaust passage via afirst exhaust manifold; and opening a first valve disposed in a flowpassage coupled between an intake passage and a second exhaust manifold,where a second set of exhaust valves are coupled exclusively to thesecond exhaust manifold. In a first example of the method, thedeactivating all valves of the first set of exhaust valves and openingthe first valve occurs after a final cylinder fires following therequest to shut down the engine. A second example of the methodoptionally includes the first example and further includes, wherein therequest to shut down the engine is a start/stop shutdown requestresponsive to a vehicle in which the engine is installed being stoppedfor a threshold duration but not keyed off. A third example of themethod optionally includes one or more of the first and second examples,and further includes, during deactivating all valves of the first set ofexhaust valves and opening the first valve, recirculating gases fromengine cylinders to an intake manifold via the second set of exhaustvalves and the flow passage. A fourth example of the method optionallyincludes one or more of the first through third examples, and furtherincludes, in response to a request to restart the engine and at aninitial cranking operation, reactivating the first set of exhaustvalves. A fifth example of the method optionally includes one or more ofthe first through fourth examples, and further includes, wherein therequest to restart the engine is generated in response to an increase intorque demand from a stopped position of a vehicle in which the engineis installed.

A system for an engine includes a first exhaust manifold coupled to afirst set of exhaust valves and an exhaust passage including a catalyst;a second exhaust manifold coupled to a second set of exhaust valves andan intake passage, upstream of an intake throttle disposed in the intakepassage, via an exhaust gas recirculation (EGR) passage including afirst valve; a secondary flow passage including a second valve andcoupled between the second exhaust manifold and an intake manifold,downstream of the intake throttle; and a controller including memorywith computer-readable instructions for: in response to a request toshut down the engine, adjusting one or more of an activation state ofthe first set of exhaust valves and a position of each of the intakethrottle and the second valve. In a first example of the system, thecomputer-readable instructions further include instructions for, whenthe request to shut down the engine is generated in response to akey-off event where a vehicle in which the engine is installed is put inpark and turned off, closing the intake throttle and opening the secondvalve. A second example of the system optionally includes the firstexample and further includes, wherein the computer-readable instructionsfurther include instructions for, after closing the intake throttle andopening the second valve, opening the first valve and opening the intakethrottle in response to rotation of the engine stopping. A third exampleof the system optionally includes one or more of the first and secondexamples, and further includes, wherein the computer-readableinstructions further include instructions for, when the request to shutdown the engine is generated in response to a vehicle in which theengine is installed being stopped but not keyed off, deactivating thefirst set of exhaust valves and opening the first valve. A fourthexample of the system optionally includes one or more of the firstthrough third examples, and further includes, wherein thecomputer-readable instructions further include instructions forreactivating the first set of exhaust valves in response to a request torestart the engine and upon engine cranking A fifth example of thesystem optionally includes one or more of the first through fourthexamples, and further includes a turbocharger including a turbine andcompressor, the compressor positioned in the intake passage between theintake throttle and where the EGR passage couples to the intake passage,the turbine positioned in the exhaust passage upstream of the catalyst.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method for an engine, comprising: inresponse to a request to shut down the engine: closing an intakethrottle and opening a first valve disposed in a secondary flow passagecoupled between an intake manifold, downstream of the intake throttle,and a first exhaust manifold coupled to a first set of exhaust valves toroute unburned hydrocarbons to a catalyst disposed in an exhaust passagecoupled to a second set of exhaust valves.
 2. The method of claim 1,further comprising, during the closing the intake throttle and openingthe first valve, closing a second valve disposed in an exhaust gasrecirculation passage coupled between the first exhaust manifold and anintake passage, upstream of the intake throttle.
 3. The method of claim2, further comprising, in response to the engine stopping rotating,opening the second valve and opening the intake throttle.
 4. The methodof claim 3, wherein opening the second valve and opening the intakethrottle includes first opening the second valve and then opening theintake throttle.
 5. The method of claim 1, wherein the request to shutdown the engine is a key off request generated in response to anoperator turning off a vehicle in which the engine is installed.
 6. Themethod of claim 1, further comprising operating the first set of exhaustvalves at a different opening and closing timing than the second set ofexhaust valves.
 7. The method of claim 1, further comprising routing theunburned hydrocarbons from the first exhaust manifold, through thesecondary flow passage, into the intake manifold, through enginecylinders, and to the catalyst via the second set of exhaust valveswhile the intake throttle is closed and the first valve is opened. 8.The method of claim 1, wherein the exhaust passage is coupled to asecond exhaust manifold, the second exhaust manifold coupled to thesecond set of exhaust valves.
 9. A method for an engine, comprising: inresponse to a request to shut down the engine: deactivating all valvesof a first set of exhaust valves configured to flow exhaust to anexhaust passage via a first exhaust manifold; and opening a first valvedisposed in a flow passage coupled between an intake passage and asecond exhaust manifold, where a second set of exhaust valves arecoupled exclusively to the second exhaust manifold.
 10. The method ofclaim 9, wherein the deactivating all valves of the first set of exhaustvalves and opening the first valve occurs after a final cylinder firesfollowing the request to shut down the engine.
 11. The method of claim9, wherein the request to shut down the engine is a start/stop shutdownrequest responsive to a vehicle in which the engine is installed beingstopped for a threshold duration but not keyed off.
 12. The method ofclaim 9, further comprising, during deactivating all valves of the firstset of exhaust valves and opening the first valve, recirculating gasesfrom engine cylinders to an intake manifold via the second set ofexhaust valves and the flow passage.
 13. The method of claim 9, furthercomprising, in response to a request to restart the engine and at aninitial cranking operation, reactivating the first set of exhaustvalves.
 14. The method of claim 13, wherein the request to restart theengine is generated in response to an increase in torque demand from astopped position of a vehicle in which the engine is installed.
 15. Asystem for an engine, comprising: a first exhaust manifold coupled to afirst set of exhaust valves and an exhaust passage including a catalyst;a second exhaust manifold coupled to a second set of exhaust valves andan intake passage, upstream of an intake throttle disposed in the intakepassage, via an exhaust gas recirculation (EGR) passage including afirst valve; a secondary flow passage including a second valve andcoupled between the second exhaust manifold and an intake manifold,downstream of the intake throttle; and a controller including memorywith computer-readable instructions for: in response to a request toshut down the engine, adjusting one or more of an activation state ofthe first set of exhaust valves and a position of each of the intakethrottle and the second valve.
 16. The system of claim 15, wherein thecomputer-readable instructions further include instructions for, whenthe request to shut down the engine is generated in response to akey-off event where a vehicle in which the engine is installed is put inpark and turned off, closing the intake throttle and opening the secondvalve.
 17. The system of claim 16, wherein the computer-readableinstructions further include instructions for, after closing the intakethrottle and opening the second valve, opening the first valve andopening the intake throttle in response to rotation of the enginestopping.
 18. The system of claim 15, wherein the computer-readableinstructions further include instructions for, when the request to shutdown the engine is generated in response to a vehicle in which theengine is installed being stopped but not keyed off, deactivating thefirst set of exhaust valves and opening the first valve.
 19. The systemof claim 18, wherein the computer-readable instructions further includeinstructions for reactivating the first set of exhaust valves inresponse to a request to restart the engine and upon engine cranking.20. The system of claim 15, further comprising a turbocharger includinga turbine and compressor, the compressor positioned in the intakepassage between the intake throttle and where the EGR passage couples tothe intake passage, the turbine positioned in the exhaust passageupstream of the catalyst.